After shares of Facebook (NASDAQ:FB) rallied strongly over the past six months, largely due to analyst upgrades, there has been a recent rise in the number of analysts making bear calls on the stock now that it's at a higher price point.

In this video, Motley Fool senior technology analyst Eric Bleeker highlights some of the current concerns, such as waning user engagement and fears that Facebook's recent successes in mobile advertising may be cannibalizing its desktop revenue. He tells us why these fears are warranted, but says that he likes seeing Facebook sell-offs, because they bring the stock down to a great entry point for investors who see it for what it could be one day: the most powerful advertising platform in history.