Facebook ( FB) has built up some impressive momentum over the course of the summer. I've made it no secret in the past that the social network isn't exactly my favorite stock -- but it's hard to argue with the market's recent love affair with FB. By far, Facebook ranks as the largest social networking site in the world: More than 600 million people use Facebook every day, and a billion use it each month. As the firm gets better at monetizing that enormous user base, the firm should grow into its lofty valuation. >>4 Tech Stocks to Trade (or Not) One of Facebook's biggest detractors is that, unlike other Internet businesses such as Google ( GOOG) or LinkedIn ( LNKD), the firm has to basically derail what its users are doing to earn advertising revenues from them. But the firm is trying to combat that by brute force; with such a massive user count, it can afford to only make money off of a tiny percentage of its users. The highly targeted nature of FB's data should help the firm charge more for space on the site. It's also gaining revenues more directly through premium online games like those made by Zynga ( ZNGA). Mobile is an exciting growth avenue for Facebook. The firm has been growing its mobile revenue at a breakneck pace, and demographic shifts toward using portable devices should make that mobile monetization all the more important to Facebook's overall value in the years ahead. More than anything else in September, market momentum is the reason to get behind Facebook. This stock has gone from a Wall Street punch line to a Wall Street darling, and there's still money on the table.