LinkedIn ( LNKD), on the other hand, has posted some stellar numbers in 2013 -- and shares have doubled over that time as a result. The professional social network boasts more than 218 million members, a growing contingent of whom are based outside the U.S. LinkedIn is investors' favorite social networking stock, and for good reason: it's the only one that actually makes money by helping its users do what they were trying to do when they logged in. >>5 Stocks Under $10 Set to Soar While other social media firms earn revenue by distracting their users from what they're trying to do (and getting them to click on ads while stalking their friends, for instance), LNKD makes money by helping users with the exact task they're trying to accomplish: find a job, network or hire someone. That seems like a small distinction, but it's core to LinkedIn's ability to maximize the money it makes off of each user. That difference comes through right in the numbers: LNKD is able to earn more money per user and better engage its user base than any of its social networking peers, around $8 per average user. That's a full 45% higher than Facebook's ( FB) per-user revenues. I've said before that LinkedIn isn't a bargain - and that's true. It's the best social networking stock by far, but its price tag is sky-high too. But what LNKD lacks in value, it makes up for from a momentum standpoint. For now, this Rocket Stock isn't showing any signs of slowing down its climb.