Gaia Online, an online world and social network aimed at teens, has raised $11 million in a Series C funding round led by Institutional Venture Partners. Since our Virtual World Roundup last summer, the site has seen impressive growth, with a reported 5 million unique users monthly.

Gaia Online is a self-described “teen hangout” that mixes elements of an avatar-based virtual world with mini-games, a social network, and a community forum. Members are rewarded for participating on each component of the site with an online currency (Gaia Gold) that can be used to purchase in-game virtual goods. Much of the site’s traffic comes from its forum, which ranks among the most active on the internet.

Gaia will likely use the funding to continue development on its MMO (massively multiplayer online game), that it plans to release this summer. The MMO will offer users a chance to interact in a persistent world (similar to World of Warcraft) rather than its existing temporary rooms. Other competitors in this space include Habbo Hotel and Club Penguin.