Billboard welcomes a new chart to its ever-growing menu with the launch of the Social 50, Presented by ZYNC from American Express®, which ranks the most active artists on the world's leading social networking sites. Rihanna tops the Social 50 in its debut week, followed by Justin Bieber, Eminem, Lady Gaga and Nicki Minaj, respectively, to round out the top five.

See the Entire Social 50 Chart

Serving as a complement to Billboard's existing weekly rankings, the Social 50 chart will tally artists' popularity using a formula blending their weekly additions of friends/fans/followers, along with weekly artist page views and weekly song plays on MySpace, YouTube, Facebook, Twitter and iLike. Data from these sites is gathered and provided to Billboard by social music tracking service Next Big Sound.

The chart's recipe also includes a unique metric that measures the ratio of page views-to-fans/friends on YouTube and MySpace, both of which allow such interactions.

The Social 50 emphasizes friends/fans behavior above other activities, followed by artist page views and song plays. The final ranking also includes a unique metric measuring the ratio of page views to fans.

Rihanna's Only Girl Reaches No. 1 on Hot 100

The chart's inaugural leader Rihanna is coming off a chart-topping week on the Hot 100 with "Only Girl (In the World)" from her new album "Loud," which debuted at No. 3 on the Billboard 200. Rihanna has placed two songs atop the Hot 100 in the past four weeks. Her duet with Drake, "What's My Name?," hit No. 1 earlier this month. Rihanna arrives at her No. 1 Social 50 ranking by leading in new friends/fans/followers for the week, while ranking fourth in total page views. Justin Bieber, who lands at No. 2 on the chart, leads all artists in weekly page views.

"The Social 50 provides a weekly snapshot of the artists with whom music fans engage with the most in the social arena, which in today's world is a significant validation of their investment in an act," states Billboard director of charts Silvio Pietroluongo. "The chart is a logical complement to Billboard's other popularity rankings."

"We continue to adapt the way we chart the changing landscape of music," says Billboard Editorial Director, Bill Werde. "The Social 50 is yet another step in the evolution of Billboard and an important response to our changing times."

"The volume of online activity that top artists now receive is too big to ignore," says Next Big Sound CEO, Alex White. "We are thrilled that social music activity now receives the same emphasis as the music charts for which Billboard is synonymous."

The Social 50 will appear in the print pages of Billboard as well as on billboard.com and billboard.biz on a weekly basis.