SAN JOSE, Calif. — In a sign that social networks and virtual worlds are beginning to meld, Gaia Online, the popular virtual playground for teens, will announce Tuesday a connection to its site from inside social network Facebook.

Gaia chief executive Craig Sherman said the new feature, to be launched as a software application on Facebook, will let Gaia members enter the virtual world and keep track of their Facebook friends while there.

Both virtual worlds and social networks are popular online locations considered part of the so-called Web 2.0 wave of Internet sites that permit greater user interaction. Social networks let users develop lists of friends while virtual worlds let people adopt personal avatars and enter animated cyberworlds through their computers.

The blending of the two has been anticipated for some time. But with this introduction by Gaia of San Jose, the merging may be starting to take place.

Gartner analyst Andrew Frank said he was not aware of other virtual worlds linking to social networking sites. "I could see how that could spark more interest in virtual worlds," he said.

Gaia, which comScore Media Metrix says had 1.7 million users in December, released a similar application for the Bebo social network Dec. 12, and Sherman said about 100,000 people have installed the application and created an avatar.

The Facebook application could have a greater impact because the Palo Alto company has many more users: Almost 35 million in December compared with San Francisco-based Bebo's 4 million, according to comScore figures.

"We want to extend the Gaia experience to where teens are," Sherman said. "We want to be everywhere."

Gaia is a site for people from 13 to 22 years old.