Rihanna's 'S&M' Sizzles on Social 50 Chart ....Billboard.com

This week on the Social 50 chart, Rihanna returns to No. 1, Selena Gomez jumps 27-13 while Tyler Ward and Chris Brown both make handsome re-entries.

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After a month's absence from the top of the list, Rihanna returns to the top -- a familiar perch for the diva, who has now spent five non-consecutive weeks at No. 1. She posted significant gains in week-over-week Twitter followers (up 24%), fans of her official YouTube channel (up 38%) and YouTube views (61%). There's no doubt that the debut of her buzzed-about music video for "S&M" drove up her social stats this week -- uploaded a week ago, the clip has already registered nearly 10 million views.

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The Social 50 ranks the most active artists on the world's leading social networking sites -- YouTube, Facebook, Twitter, MySpace and iLike -- using a formula blending weekly additions of friends/fans/followers along with weekly artist page views and weekly song plays.

Selena Gomez is on the verge of breaking into the top 10 for the first time, as she rallies 27-13 with gains in Twitter followers and YouTube channel views. Gomez took to you YouTube last week -- as did Taylor Swift (No. 12, down three) to profess their fandom for Nicki Minaj (who moves 13-7). Gomez and Swift can be found -- separately -- on YouTube rapping to Minaj's "Pink Friday" album cut "Super Bass." The two most popular clips racked up more than 2 million views in their first five days of release.

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As Minaj motors into the top 10, she's joined by another returning-to-the-top-10 act: Linkin Park, who climbs 12-10. As for the rest of the top tier, Akon rises 3-2, Lady Gaga is up 4-3 and Shakira tip-toes
5-4. Justin Bieber somewhat shockingly drops 5-1 -- but we expect he'll move back up next week once the full impact of his new movie, "Never Say Never," reaches the masses after it opens in theaters this weekend (Feb. 11). Eminem climbs 7-6, Katy Perry falls 6-8 and Michael Jackson rises 10-9.

At No. 30, Tyler Ward re-enters thanks to big YouTube gains. His channel earned a 16% week-over-week increase in subscribers while his videos captured a 59% leap in views. Credit is likely due to his uploading of two new videos within the past two weeks: a cover of Wiz Khalifa's "Black and Yellow" (more than 500,000 views) and Jessie J's "Price Tag" (200,000-plus views).

Chris Brown is also back on the list, re-entering at No. 31. Credit that to the the social buzz surrounding his new hit single "Look At Me Now," which reached digital retailers last week. The song debuts at No. 11 on the Billboard Hot 100 this week -- the singer's highest charting effort since August of 2008, when "Forever" peaked at No. 2.