Nov. 26 (Bloomberg) -- A negative review or comment on the Twitter, Facebook or Youtube Web sites can lose companies as many as 30 customers, according to a survey by Convergys Corp.

A customer review on one of the sites reaches an average audience of 45 people, two-thirds of whom would avoid or completely stop doing business with a company they heard bad things about, Convergys said, citing its own survey.

Web and video posts are feeding a new form of “silent attrition, where customers switch companies without complaining directly,” Frank Sherlock, senior vice president at Cincinnati- based Convergys, said at a conference in London yesterday.

The provider of customer call-center services commissioned a survey of 2,000 British consumers, one in three of whom said they put their bad customer experiences on the Internet.

The influence of a post on Youtube, the world’s most popular video-sharing site which is owned by Google Inc., can have a “definitive measurable impact,” Sherlock said.

To contact the reporter on this story: Sarah Shannon in London at sshannon4@bloomberg.net.

Last Updated: November 25, 2009 19:00 EST