When radiation oncologist Michael Tomblyn recently saw a 21-year-old patient whose eye was protruding from its socket, he turned to his fellow physicians for help. Dozens of doctors offered suggestions, including fungal infection, HIV-associated lymphoma or a cocaine-associated sinus problem, eventually steering him toward the correct answer: rhabdomyosarcoma, a fast-growing cancer most often observed in young children.

The diagnosis didn't take place in a doctor's lounge. It happened on Sermo.com, a social-networking site for licensed physicians, which Dr. Tomblyn and 25,000 doctors like him visit regularly to consult with colleagues specializing in areas from dermatology to psychiatry.

"It is a way for us to commiserate and know we are still talking to others like us," says 36-year-old Dr. Tomblyn, who works for the University of Minnesota Medical Center.

Social networking, popularized by teens sharing information with their friends online on Web sites such as Facebook Inc., is now blooming in the business world, thanks to new social networks that enable professionals and executives in industries such as advertising and finance to rub virtual elbows with colleagues.

Millions of professionals already turn to broad-based networking sites like LinkedIn to swap job details and contact information, often for recruiting purposes. Business executives also have turned to online forums, email lists and message boards to sound off on information related to their industries.