Photo sharing app had only 15 million users in January 2012, has grown by over 200% in four months.

Allie Walker Allie Walker on May 3, 2012. @NYC_Allie

2012 has been a big year for Instagram, and the photo sharing app has just hit another major milestone- 50 million users.  The site has grown substantially during the first four months of the year, starting off 2012 with only 15 million users. Fast Company