Within just 3 months of its launch, BarbieGirls.com has become the fastest growing virtual world, touting four million registered users.

The site is growing by an average of 45,000 girls per day (compare that to social networking site Facebook's 10,000 a day, which is considered very impressive).

This week see the launch of the much discussed Barbie Girl MP3 playing device which will promote the site even more.

The multi-functional Barbie Girl product is a "key" to unlock exclusive play features and "trillions" of character and room combinations on the site.

It will allows users on BarbieGirls.com to adopt pets, buy clothing and accessories and enter exclusive hangout spots within the world.

The future is pink.