Instagram has 150 million active monthly users

"Today we’re excited to announce that Instagram has grown to a community of more than 150 million people capturing and sharing moments every month.
Whether it’s documenting protests in Egypt, sharing the trip of a lifetime across the United States or snapping #petselfiez, this community continues to surprise us every day with your creativity, sense of adventure and unique perspectives on the world.
As the community continues to grow, it’s becoming more global too — now more than 60% of you are from outside the United States. Whether you’re in Moscow or Hong Kong, Berlin or Reykjavik, we’re more committed than ever to bringing you the best Instagram experience possible.
To the 50 million of you who’ve joined in the last six months, welcome. And from our team to all 150 million of you, thank you for making Instagram great. We can’t wait to see what you’ll create next."
Source:  Blog post by Instagram, 8th September 2013
Earlier - 130 million announced on 21st June 2013