While Facebook may be the biggest social network in the world, it isn't exactly the place where teens like to spend their virtual time nowadays. According to a survey conducted by investment bank Piper Jaffray, Instagram is the new cool when it comes to teens' favorite social networks.

Of the 72,000 teens surveyed, 76 percent said they use Instagram, up from 69 percent in the spring of this year. By comparison, just 45 percent of teens said they use Facebook, down from 72 percent a few months ago.

Meanwhile, Twitter's popularity also went down, with only 59 percent of respondents indicating use of the microblogging service, down from 63 percent in the spring. While Instagram, Twitter, and Facebook held the first three spots, Pinterest and Tumblr came in fourth and fifth, respectively.

One of the major reasons of teen exodus from Facebook is said to be the presence of a large number of adults on the social network. "As every parent knows, once Mom and Dad get involved in something the kids likes, that thing becomes almost instantly uncool", said Dan Olds, an analyst with The Gabriel Consulting Group.

Although Facebook boasts of over 1 billion users worldwide, teenagers have been drifting away from the social network for quite some time now. Last year, then Facebook's chief financial officer David Ebersman also admitted that the social network was struggling to maintain teenagers' attention.

While exodus to Instagram shouldn't be a big problem for Facebook, as it already owns the photo-centric service, the company has taken steps to lure teens back. In February this year, Facebook acquired popular mobile messaging service Whatsapp, and in June it released Slingshot, a Snapchat competitor. Earlier this week, there were also reports that the company is building an anonymous mobile chat app.