Shawn Mendes

Shawn Mendes photographed by Blossom Berkofsky on July 9, 2014 at Industria in New York.

Blossom Berkofsky

Shawn Mendes — a sweet-voiced, dreamy-faced 15-year-old Canadian singer whose name, at the moment, is inextricably connected with the words "Vine sensation" — sits on a stool in a rehearsal room on Manhattan's West side. Tom Jackson, a long-haired veteran "performance coach" who worked extensively with the teen Taylor Swift, listens intently, a notebook crammed with illegible scrawl next to him, while Mendes runs through his song "The Weight," one of the tracks from his debut EP, "Life of the Party," which arrives on Island July 28.

Tonight in this room, Mendes will play an EP release party for about 60 label and management execs, press and others. Two weeks from today, he'll be on "Live With Kelly and Michael,"and the day after that he begins his first-ever tour — playing solo, opening 30 dates for Austin Mahone — at the 11,700-capacity Freeman Coliseum in San Antonio. He'll celebrate his 16th birthday during a day off from the tour.

Mendes and Jackson have been working together for less than two days, and some polite tussling for the upper hand is going on. Mendes, who possesses striking poise for his age, isn't quite bristling at Jackson's direction, but he's pushing back. He's also playing the song too fast, with a staticky energy that reminds you he's just 15. Jackson holds up his hand.

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"Tell me about this song," he says. "Where does it come from? What's it about?"

Mendes leans back a bit. "There's a little bit of anger behind it," he says. "It's about your girlfriend cheating on you with your best friend, and now she wants to come back, and you say, 'I want you back, but I just can't get past this.'"

"That's perfect," Jackson says. "There's gonna be three places [in the set] where you need to talk to the audience, and this is one of them. 'This song is about a girl' — 'YAAY!' — 'I really liked this girl' — 'AWW!' — 'but she cheated on me' — 'AWWW!' — 'with my best friend' — AWWWWW!' Don't be in a hurry: Wait for the response."

"I don't wanna, like, script it out," Mendes says. "I get weird with that."

"It's cool, let's just try it…"

Jackson conducts, cajoles and gesticulates like a cross between a cool gym teacher, the voice coach in The King's Speech, and Christina Aguilera, adding lots of "dude"s along the way. Twenty-five minutes later, the song and its spoken introduction have nuances and a flow that most people probably think a singer just does, if they think about it at all. Jackson and Mendes work on the song's ending, testing how many times to repeat the last line, throwing in an anguished vibrato flip, a Timberlake-ian vamp.

"Yeah!," Jackson says. "Now there's space in there, dude. And once you get past the rush of being onstage in front of 8,000 people and all that, you're gonna be listening to them — you can riff on it if they're with you; if they're not, you shut it down."

"Wow, that feels really good," Mendes says. "So take it from the first verse?"

At the moment, Shawn Mendes is a prototype for the modern pop star, occupying a kind of subduction zone where the new music business meets the old. He's part of the first generation to grow up with and on social media. He learned to sing more from watching YouTube covers than from listening to the original versions, and he taught himself to play guitar via YouTube. There were traditional things like his school's glee club and acting lessons (he played Prince Charming, fittingly enough), but he got where he is today almost entirely from his bedroom in Pickering, Ontario.

He'd been uploading cover videos to YouTube for a couple of years when, one day last summer, he noticed that no one seemed to be doing them on Vine.

"I was sitting in my bedroom and my sister came in and I said, 'Hey, can you record this?,'" he remembers. He did a six-second clip of the chorus from Justin Bieber's "As Long as You Love Me," and "it blew up overnight": 10,000 likes and as many followers by morning. He kept posting covers, had 200,000 followers by October (when he drew a couple of thousand fans to a meetup gig in Toronto), and played the Dallas edition of Magcon (a tour for social-media celebs) in November.

One night in January Andrew Gertler, who manages rapper Rockie Fresh and, until recently, worked in Warner Music Group's D2C division, was watching The Voice and heard A Great Big World's "Say Something."

"I thought it sounded like a song people would cover, went on YouTube, and Shawn's was the first one to come up," he recalls. "It had a good amount of views, but it was more like, wow, this kid is really talented, so I reached out to his mom, who at the time was the contact on his website."

Gertler, 25, showed the clip to his friend and former fellow Atlantic marketing intern Ziggy Chareton, now an Island A&R rep (the two interned for Eric Wong, now an EVP at Island). He convinced Mendes' parents to bring him to New York, and the two of them brought him to meet with Island president David Massey.

"I knew within the first two minutes that he's a star," Massey says. "It was just undeniable."

During that first visit, Gertler and Chareton introduced Mendes to a couple of young songwriters, Ido Zmishlany and Scott Harris. The three got along and then went into the studio. "They had cut 'Life of the Party' before we took any meetings," Gertler says. Other labels were interested — Atlantic, RCA, Republic, Warner — but "Shawn felt comfortable at Island and really connected with David Massey."

As the weeks went by, Mendes kept posting clips — Ed Sheeran's "Give Me Love," Lana Del Rey's "Summertime Sadness," so many Vines that there's a 20-plus-minute compilation — and the audience kept growing. In April he won Ryan Seacrest's "Best Cover Song" contest with "Say Something" (1.6 million views). He's currently at 1.31 million Twitter followers, nearly 1.4 million on Instagram, and 2.8 million on Vine. He even flew out to L.A. and had dinner with Sheeran, a meeting that was arranged by publicist Jason Davis, another member of Gertler's Atlantic-intern posse.

Somehow, through it all, Mendes managed to finish his sophomore year of high school (he'll have a private tutor this fall). "I was finding it very difficult to sit in class and focus because my mind kept wandering," he admits. "I had to say, 'When I'm in New York, that's the place to focus on [the music career], but now I'm gonna focus on chemistry.'"

Meanwhile, his team focused on "Life of the Party." Massey decided the best thing for Island to do, initially, was to leave it to the fans. On June 26, the label put the song on iTunes and stepped back.

"We sold 200,000 in the first 10 days," Massey says. "We decided to put it online with no marketing or airplay because we wanted to understand his fanbase and how it would behave. We released the song at 11:15 p.m., and it was No. 1 at midnight. Within the first 24 hours, we had exceeded 100,000. That's true fan engagement and true conversion, from being a fan to putting down money."

The song also entered the Hot 100 at No. 24 in its first week. "I think the reason it might be sticking is because it's so relatable for teenagers," Mendes says. "Lots of teenagers are finding it hard to figure out who they want to be, and this song really pushes it into your head that you're gonna be awesome who you are."

Just four days after the song was released, Mendes played a pop-up concert in Times Square that was unexpectedly unhinged, drawing several hundred people (originally scheduled for Central Park, it had to be moved because of the crowds). Fan videos show dozens of girls singing along with "Life of the Party," a song that they'd known for 96 hours, at most. Another fan video is called "Me squeezing Shawn Mendes' butt," which happens as Mendes tries, very politely, to get through the crowd.

"It's progressively getting more and more [crazy], but I think my fans are very respectful," Mendes says. "I will always take pictures with fans, but they back off if they can tell I'm tired. There doesn't need to be a [bodyguard]."

"His life has changed very quickly," Massey says. "Times Square was really quite intense and a little crazy, but the way he handled it and kept everyone under control was really remarkable for someone who's not yet 16. He's consistently like that, whether he's meeting the chairman of a company or dealing with 600 girls."

The focus for the summer is the EP and tour, but in the fall work will begin on his album, which is targeted for release late this year or early next; possible collaborators include Martin Terefe (Jason Mraz, Train's "Hey, Soul Sister") and Julian Bunetta (One Direction, Jason Derulo). And as things progress, the older models of the record business will kick in.

"Obviously there will be a [larger] plan and we will widen his fanbase from its core through TV, press, all the traditional methods," Massey says, "because the modern methods have already been achieved."

Back at the rehearsal studio, three hours later, the small room is packed with people. Massey introduces "our newest signing," promising that "you're all going to see how talented he is." Mendes straps on his guitar and warns that his voice might be scratchy because he's been rehearsing all day.

It's not. He kills "Life of the Party," and then puts down his guitar and joins his own party, one very different from the one he just sang about.