Instagram hit a milestone this week, logging more than 400 million monthly users, solidly surpassing rival Twitter.
"Given that Facebook owns Instagram, that certainly makes them the king of the social networking mountain," said Dan Olds, an analyst with The Gabriel Consulting Group. "Instagram is aimed squarely at mobile devices, and that makes it very easy for users to shoot and post very quickly. It also has the patina of 'cool' with hip users -- mainly arising from young users adopting it as their own."
Instagram is gaining momentum. In December of last year, the company said it reached the 300 million monthly user mark. Less than a year later, the site has added another 100 million active users.
Despite the surge in monthly users, Instagram is still far behind Facebook, the world's largest social network with more than 1 billion worldwide users.
However, the numbers put Instagram beyond Twitter, which in June reported 316 million active monthly users. Instagram is also well ahead of Google+, which reportedly has about 300 million active monthly users.
"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 wrote in a blog post. "Our community has evolved to be even more global, with more than 75% living outside of the U.S. To all the new Instagrammers: welcome!"
Among the last 100 million to join, more than half live in Europe and Asia, the company noted. The countries that added the most Instagram users include Brazil, Japan and Indonesia.
"Instagram surpassing Twitter in terms of monthly users is a pretty big deal and will probably surprise quite a few people," Olds said. "Instagram has typically been seen as skewing more toward young people . The fact that it suddenly has more users than Twitter means Instagram must be breaking through with adults, as well."
Twitter's user growth and the strength of its advertising business has raised concerns among investors since the company when public in 2013.