Girls who love fashion are pushing Stardoll to new membership heights. Today, the Swedish company announced that its membership base has surpassed 50 million registered users.

Stockholm-based Stardoll created a site where members can create their own MeDoll avatars, design their own fashions, and furnish their own virtual suites. They can engage in social play and purchase virtual items for their avatars to wear. Since its launch four years ago, the user base has grown to 12.25 million unique visitors a month. The members come from 230 territories and converse in 17 languages. New members are signing up at a rate of 45,000 per day. The core audience ranges in age from 9 to 17.

The growth tells us how broad the Internet’s reach has become, since girls were not early driver’s of the web audience. Rivals include fashion-oriented virtual character sites such as Nurien to general-purpose virtual worlds such as Second Life. Investors include Sequoia Capital and Index Ventures.