7. Austin Mahone: 21 Under 21 (2013)

Austin Mahone

Last Year's Ranking: Ones to Watch

Birthdate: April 4, 1996 (age 17)

Why He's Hot: Austin Mahone has officially crossed over after spending years growing a fan base through YouTube performance and social media. This year, the rising pop singer scored his first-ever Hot 100 single with the RedOne-produced scorcher "What About Love," and snagged an opening spot on one of the year's biggest tours -- Taylor Swift's "Red" run. Mahone punctuated a hugely successful summer by performing on the MTV Video Music Awards pre-show, and then winning the Artist To Watch VMA hours later in front of millions of viewers. With a debut album coming soon on Chase/Republic, Mahone could climb even higher on next year's 21 Under 21 ranking.