Still thinking about building a social-networking site for your employees? Sure they haven't started without you? Check Facebook, you might get a surprise.

As companies grapple with whether, and how, to offer a social-networking platform for their workers, some are realizing that if they don't act quickly, their workers will go ahead and do it anyway. And that can mean forfeiting control over what content gets posted where, and who can see it.

"Do you really want Facebook to manage it for you in the outside world, or do you want to do it yourself so you have control?" said Duane Nason, a lead Web engineer with The Gap clothing retailer. "If someone posts something to MySpace and you want it taken down, what's their policy on that?"

Nason was at the Web 2.0 Expo this week to learn more about how social networking, mashups and other new technologies can be applied at his company. He's one of many representatives from large companies at the conference who are grappling with similar questions.

Nason, who helps run The Gap's Web site and intranet portal, threw up a wiki recently for use by his small circle of colleagues. He was surprised to discover later that other employees in the company -- mostly younger staff in junior positions, he said -- had been entering their profiles and using the wiki, even though it hadn't been marketed internally. "They just found it and started using it," he said.

He also noticed that, as with many large companies, employees at The Gap have started to form their own groups on Facebook. Big companies should develop a social-networking strategy before their employees do it for them, he advised.

An IT manager with another well-known retail company agreed. "If you don't do it for them, there are enough tools out there that they're going to do it themselves," said the manager, who asked not to be identified because he is not authorized to speak publicly for his company, and because his company is still unsure of its strategy.

He was at Web 2.0 to explore ways of using social networking to build a closer bond with customers. E-commerce sites are not good for building a community, he said, but a social network could allow customers to form their own groups and discuss products they are interested in. He is also interested in widgets that provide updated information about special offers, for example, to a user's desktop.