This week marks the one-year anniversary of the launch of Billboard's Social 50 chart, our tally that ranks the most active artists on the world's leading social networking sites. While a good number of acts have never left the tally (we're looking at you, Justin Bieber, Lady Gaga and Rihanna), there have been quite a few new artists that notched impressive peaks on the chart. These include viral stars like Pomplamoose (who peaked at No. 29), George Watsky (No. 13), Rebecca Black (No. 9), Karmin (No. 15) and Kina Grannis (No. 49).

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The chart rankings are determined by activity monitored on YouTube, Vevo, Facebook, Twitter, MySpace and iLike, using a formula that blends weekly additions of friends/fans/followers along with weekly artist page views and weekly song plays.

Let's catch up with a few of the viral acts that broke onto the Social 50 chart in the past year:

Things on the Pomplamoose front have been relatively quiet, perhaps, because singer Nataly Dawn has been working on her first solo album, which is due out in 2012. She successfully gained funding for the project through the crowd funding site Kickstarter. Fellow member Jack Conte has been releasing solo projects too, with his latest song "I Wonder Where Moments Go" premiering on YouTube Oct. 8. The group released a video for their song "Bust Your Knee Caps" on Oct. 11, which has since earned 359,000 YouTube views.

Their most recent viral video, however, dates back six months ago to May 10. They uploaded their upbeat rendition of the theme song from the popular mobile game Angry Birds to YouTube.

Last time we heard from fast-rapping George Watsky he had released his mixtape "A New Kind of Sexy" on Aug. 1 and premiered a short video cover of "Show Goes On" by Lupe Fiasco on Aug. 17. That day, Watsky also made an appearance in the popular YouTube series Epic Rap Battles of History. Since then, his channel has been rather quiet, save for a battle rap where to calls out Childish Gambino.

Rebecca Black is back, though she hasn't re-entered the tally since the viral success of the video for the single "Friday." The video for her latest single "Person of Interest" debuted on Nov. 15.

YouTube cover stars Karmin debuted on the tally on Aug. 11 with the duo's cover of Demi Lovato's "Skyscraper." Since then, their most successful cover has been "Lighters" by Bad Meets Evil. Karmin also recently released their original single "Crash Your Party" on Nov. 8, off their upcoming album, which is due out in 2012.

Lastly, we have Kina Grannis, who debuted on the tally rather recently, thanks to her viral video for "In Your Arms." The jelly-bean infused clip has earned more than 3 million YouTube views since its Nov. 2 debut. She also made an appearances on "The Ellen DeGeneres Show" (Nov. 15) and Billboard's new webseries, "TMI: The Music Insider" (Nov. 17). The recent media attention has helped her "Stairwells" album zip up our Heatseekers chart, where it roses 21-4 last week (up 124% in sales).

On this week's chart, there are eight acts in the top 10 who have never left the chart after 52 weeks. In total, sixteen artists have never stepped away from the Social 50. This week, Justin Bieber (No. 1), Adele (No. 2), and Eminem (No. 8) are non-movers, while Lady Gaga (4-3), Rihanna (6-4), Selena Gomez (9-7) and David Guetta (11-10) rise up the tally. Lastly, Shakira (5-3) and Katy Perry (6-5) slip just a bit.