NEW YORK (Reuters) - The heads of the top U.S. companies might be engaged in the boardroom, but they're switched off when it comes to social media, according to a new study that said CEOs should be more connected to their customers.

Research conducted by the blog UberCEO.com looked at Fortune's 2009 list of the top 100 CEOs to determine how many were using Facebook, Twitter, LinkedIn, Wikipedia, or had a blog -- and found they were mostly absent from the rapidly growing social media community.

The study found only two CEOs had Twitter accounts and 81 percent of CEOs did not have a personal Facebook page.

Only 13 CEOs had profiles on the professional networking site LinkedIn. Three CEOs stood out with more than 80 connections but they were all from technology companies -- Michael Dell from computer maker Dell Inc., Gregory Spierkel from technology products distributor Ingram Micro Inc., and John Chambers from Cisco Systems Ltd.

Three quarters of the CEOs did have some kind of Wikipedia entry, but nearly a third of those had limited or outdated information such as incorrect titles, or lacked sources.

Not one Fortune 100 CEO had a blog.

"It's shocking that the top CEOs can appear to be so disconnected from the way their own customers are communicating. They're giving the impression that they're disconnected, disengaged and disinterested," said Sharon Barclay, editor at UberCEO.com who runs executive PR firm Blue Trumpet Group.

"No doubt regulations such as Sarbanes-Oxley and Reg-FD make CEOs cautious about communicating freely, but they're missing a fabulous opportunity to connect with their target audience and raise their company's visibility," Barclay said, referring to financial reporting regulations aimed at protecting investors.

Social networking sites are booming, with the latest figures by Nielsen Online showing the number of minutes spent on them in the United Sates doubling over the past year.

(Writing by Belinda Goldsmith, Editing by Miral Fahmy)