Rihanna, Eminem, Bieber Top Billboard's New 'Social 50' Chart

Rihanna, Eminem, Bieber Top Billboard's New 'Social 50' Chart: 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,