As the world shifts to mobile, Facebook's current mobile advertising strategy, which includes showing sponsored stories in a user's newsfeed on their device, is simply not enough to support the company's current valuation, Greenfield said.
And what's more, said Greenfield, when it comes to pushing local advertisements to consumers on mobile devices, the social network falls short to its competitors because it is generating targeted ads based on data that just isn't that accurate.
"Facebook doesn't control your device, they don have the operating system, the operating system on mobile is really just two companies. One is Google with Android and the other isApple with iOS. Those are the companies that really know everything about you," Greenfield said.
Facebook, though, uses data pulled from a users' profile and the user's interactions on the platform, which is not the most accurate way to target local mobile ads, Greenfield said. Part of the reason Facebook is struggling and will continue to struggle in advertising is because its focus has shifted.
While Facebook went public with the intention of connecting the world to better connect consumers, its goal now is to make money, which has caused Facebook to not be as stringent in its policies as to how other companies advertise on the platform, Greenfield said.
"We are seeing companies that are being offered the opportunity, like Wal-Mart, to leverage Facebook, and we are seeing them push very, very hard for "likes" and really almost to add spam towards consumers," he said.
But more than just allowing bad advertising from companies on its platform, Facebook itself just isn't the best competitor in the mobile advertising space, Greenfield said.