Social media giant and market newcomer Twitter (NYSE:TWTR) had been enjoying quite the post-IPO run until a few weeks ago, when analysts began downgrading the company. Twitter was hit with a downgrade from Macquerie two weeks ago, then another by Morgan Stanley earlier this week. The latest blow comes from Cantor Fitzgerald, which stated that the company's big post-IPO rally had outstripped its fundamentals.

Motley Fool Senior Analyst Bryan White believes that the downgrades are coming due to a combination of fundamentals and high valuation. He doesn't think analysts want to repeat what happened with Facebook's (NASDAQ:FB) IPO, plus he acknowledges that social media advertising is still in its infancy and that Twitter has a lot to prove. 

Speaking of Facebook, Bryan thinks the social media titan makes more sense for advertisers than Twitter. It's a more proven company, and its successful development of its mobile platform is impressive. Meanwhile, Bryan would counsel patience for potential Twitter investors--although today's decline is a tempting entry point and Bryan likes the company in the long term, it still needs to prove itself with a successful earnings season or two.