It's all about Lady Gaga and Justin Bieber on Twitter, but when it comes to Facebook, Eminem wins. The rapper is the most popular artist on the site, the first to rack up 60 million fans. Rihanna is a close second with 59 million fans, E! reports, while Lady Gaga has 53 million. Compare that to Twitter, where Gaga has 27.8 million followers and Em has just 11.8 million.