It started only in March 2003 but the popular social-networking service has been expanding exponentially at a rate of 20% a week. Friendster.com absorbs real-life social groups into a large virtual network and helps users find dates and new friends by referring people to others in their network.

When you sign up, you post your photo and write something about yourself. Then you give a list of your friends and their e-mail addresses. Friendster contacts these people to join your network and when they sign up, they’re asked to confirm their relationship with you. This gains them access to your other friends and the friends of your friends, and the friends of your friends’ friends, and so on.

Danah Boyd, a U.C. Berkeley Ph.D. student researching online social networks, said Friendster is beginning to have an “unbelievable impact” on its target demographic, urban-dwelling 25- to 35- year-olds. It’s so popular that the word “friendster” has come to mean a person that someone meets or knows through the network.