LOS ANGELES — When Toyota Motor Corp. wanted to promote its new Scions to young buyers, it turned to one of the growing number of digital design companies doing business in the popular online universe "Second Life."

The firm, Millions of Us, conjured up Scion City — a futuristic urban island with a dealership that sells the cars and a racetrack where consumers' online personas can take them for virtual test drives.

"The goal is to build a community in 'Second Life' that is really engaged and really excited and really involved," said Reuben Steiger, 35, chief executive of Millions of Us, which is based in Sausalito, Calif.

Designing attractions to capture the attention of those online visitors is becoming big business as major corporations move to establish marketing footholds in 3-D virtual worlds such as "Second Life," which was founded in 2003 by San Francisco-based Linden Lab.

While it feels like a video game, with cartoonish-looking graphics, computer users easily become immersed in the action via cyber stand-ins known as avatars. Through their animated alter-egos, users can travel the simulated expanse and chat, fly, dance or even simulate sex with others.

"Five years from now, it will be near-photo quality," Steiger said. "The experience of walking in will be like stepping into a movie."

"Second Life" now boasts more than 3 million registered users worldwide, and Linden Lab estimates about 1.3 million users logged on to the realm in the past month.

Companies pitching everything from virtual T-shirts to entertainment have followed the crowd.

Since launching in July, Millions of Us has done projects for General Motors Corp., Sun Microsystems Inc., Warner Bros. Records, Microsoft Corp., 20th Century Fox, Intel Corp. and rapper Jay-Z, among others. Other major companies that have established a presence in "Second Life" include IBM Corp., Dell Inc., CNet Networks Inc. and Adidas AG.

Computer users have been gathering in 3-D, virtual environments for years using games such as "World of Warcraft" and "Star Wars: Galaxies."

Companies behind those games employ their own cadre of programmers and designers to build the worlds from scratch. Users have limited leeway, if any, to modify their virtual behavior or create new objects.

"Second Life," however, comes with a built-in interface to transform geometric shapes into just about anything, and users can take classes within the realm or use tutorials to beef up their object-building skills.

Those who take the time to learn a more advanced programming language also can write "scripts" that control the movement of avatars or how they interact with objects.

Users have created everything from flying birds to waves crashing ashore by their tropical resort. And they retain the intellectual property rights to whatever they create.

A surprising number of structures within "Second Life" are richly elaborate, with design and function on par with content seen in professionally designed games. The best simulate real-world details, such as landscaping, different textures for brick or marble, and realistic lighting effects.

Many other structures, however, are rudimentary and unpolished. Often, they are simple boxlike shapes, with few or no objects inside. Some are missing walls or are just unfinished floating slabs.

That disparity in quality is reminiscent of the early days of the Web, when just about anyone with a few HTML skills could make a personal Web site. Companies seeking more compelling presentations often turned to Web design firms.

The same dynamic has fueled demand for 3-D design houses. Dozens of willing developers worldwide are listed on the "Second Life" Web site alone.