8. LinkedInLinkedIn ( LNKD) was the first social networking site to go public, holding its IPO in May 2011 at $45 per share, reaching $122.70 at the high that day. LinkedIn proved the demand for profitable social networks. As "Facebook fever" continues, it doesn't hurt that LinkedIn just reported strong first-quarter results. Mountain View, Calif.-based LinkedIn reported earnings of 15 cents per share on $188.50 million in revenue for the quarter that ended in March. Analysts polled by Thomson Reuters were expecting earnings of 9 cents on $178.58 million in revenue. LinkedIn doesn't compete directly with Facebook, but BranchOut, a Facebook app that launched in July 2010, has been gaining traction, with more than 25 million registered users, according to its website. Shares of LinkedIn have gained 76.92% this year.