Soon, BrighterPlanet.com will feature a portable social Web application that will allow visitors to calculate the status of their carbon footprints and share what they are doing on conservation on other social platforms like Facebook.

Friends, family and colleagues can immediately see how saving the environment is important to BrighterPlanet members, Ms. Prairie said. “That’s what we find is the beauty of social networking, particularly for environmental-type causes.”

A recent study for Sage North America found that 65 percent of small businesses that used social networking sites said that they felt more comfortable doing so this year than they did last year, and 51 percent said that they had acquired and retained customers because of it.

More than 260,000 North American businesses currently use social networking to promote their businesses, Mr. King said.

In April, Sage, which has 2.9 million small and midsize business customers, introduced its own networking site, SageSpark .com. “We know we’re not the first to the game,” Mr. King said. “Our twist really is the community, tools and services.”

Other niche sites have sprouted recently, like Shustir.com.

Last week, Shustir.com introduced its virtual marketplace, which was started by two former Lehman Brothers colleagues, Shu Kim and Khanh Pham. “It matters where you spend,” Ms. Kim said, echoing the site’s catchphrase. The goal, they said, is to keep Main Street U.S.A. alive.

“We want you to spend with small businesses,” Ms. Pham said. “By doing so, 80 percent of the money goes directly back to the community.”