Instagram

With more than 100 million active users, Instagram has yet to monetize its photo-sharing social network.

Acquired by Facebook in April 2012, Instagram—one year later—has had some trouble cashing in. The company announced changes to its privacy policy last September that would have given users' data to Facebook affiliates and advertisers, as well as reserving the right to feature users' photos in advertisements. But Instagram backtracked when users protested.