Facebook (FB) shares are down almost 40% from their May IPO price. So why is the stock of everyone’s favorite Internet destination getting slammed? 

Facebook is at the point of near saturation in the U.S. People who don’t use it are quickly becoming a minority. Because of this, the site has been trying to improve its net profit per user. The company’s new platform, which includes a newly designed iPhone app and a Facebook phone created with HTC, will allow ads to be pushed to mobile users. But it hasn’t been cheap to build this new technology, which is worrying investors 

Growth is another concern. Facebook has almost one billion users, and the only way it can continue its growth rate is to get more users in Asia. But for now, Facebook is blocked by the ‘Great Firewall of China.’ CEO Mark Zuckerberg thinks that with enough growth elsewhere access to the site will eventually happen in China, but this assimilation theory doesn’t seem likely in the short run.

Facebook’s listing was a disaster, and the stock has traded lower ever since. It needs to address its ad-driven model and going-forward growth issues to overcome this rocky start.