Instagram, which Facebook purchased for $1 billion in 2012, says it has surpassed the milestone of 400 million active monthly users. Justin Sullivan/Getty Images

Instagram announced Tuesday that it has surpassed the milestone of 400 million monthly active users, showing healthy growth and proving that it is quickly turning into a moneymaking machine for its owner, Facebook.

The popular photo-sharing app's accomplishment comes just nine months since hitting 300 million users in December of 2014. The announcement is great news for advertisers, who were finally handed the keys to start using the mobile social network for visual-driven advertisements last month.

Instagram is expected to reach a solid $600 million in global ad revenue this year, but that figure is expected to see rapid growth in 2016 and then reach as much as $2.81 billion in 2017, according to eMarketer. At those figures, Instagram is expected to account for nearly 11 percent of Facebook's 2015 mobile ad revenue and as much as 28 percent by 2017.

Number of Active Social Media Users by Network | FindTheCompany

"While milestones like this are important, what really excites us is the way that visual communication makes the world feel a little bit smaller to every one of us," Instagram said in a blog posted Tuesday.

Facebook purchased the app for $1 billion in 2012. At the time, it was the largest acquisition in Facebook's history and looked like a risky move, but it became apparent quickly that Facebook had gotten a steal of a deal. Facebook itself is now at 1.49 billion monthly active users, its WhatsApp messaging service stands at 900 million users, and Facebook Messenger is at 700 million users.