More than half of the U.S. online population is made up of active online social networkers, yet advertising on these sites is still flat, according to a new report by market research firm IDC, part of International Data Group. The report calls marketers' attempts to tap into these sites' unique social nature “stillborn,” MediaWeek reported.

This report, titled “U.S. Consumer Online Attitudes Survey Results Part III,” found that more than three out of four social networking site users log on at least on a weekly basis, and 57 percent do so daily. These people also spend lots of time on the properties - more than 61 percent of users spend at least half an hour on these sites per session, and 38 percent stay for at least one hour.

“The thinking has been that the popularity of (social networking sites) will attract a big audience and generate a lot of traffic, which in turn will produce enormous amounts of user-generated content and therefore advertising inventory, without any expenses for editorial staff or content distribution deals,” according to Karsten Weide, programme director, digital Marketplace: media and advertising, IDC. “That's all proven true, except the advertising part. (These sites) have had a hard time selling this inventory,” Weide added, according to MediaWeek.

Key players, such as MySpace and Facebook, have promised advertisers highly targeted advertising, as long as users provide information including age, location, personal interests, etc.. However, IDG's study indicated that just 3 percent of users surveyed feel comfortable if publishers use their contact information for advertising.

“That idea is stillborn,” the IDC report stated, according to MediaWeek.

According to IDC, to improve ad effectiveness, social networking sites need to become more like portals, and provide users with something to do other than communicate. “That's something MySpace has gradually done over the past few years as its added more professionally produced content and video,” the study noted.