LinkedIn (NYSE: LNKD) is growing at more than two members per second. The company operates one of the best-monetized social networks in the world. An optimal mix of a premium subscription model, advertising, and human resources services has allowed the company to beat earnings expectations every quarter. However, although LinkedIn's profitability remains strong, it may be facing a revenue growth problem. The company provided lower-than-expected revenue guidance on the latest earnings call, causing shares to slump 3.3%.