Popular social networking websites like MySpace or Facebook are struggling to generate advertising revenue, a new report has suggested.

A study released by research firm eMarketer has shown that despite the "media hype" surrounding Web 2.0, many sites have been unable to use their popularity to generate funds.

In light of its findings, the agency has downgraded its prediction as to the amount advertisers are likely to spend on social network marketing this year, forecasting £1 billion worldwide, moving to £2.2 billion by 2011.

Previously, eMarketer had predicted that £2.4 billion would be spent on such promotions by 2011.

Debra Aho Williamson, a senior analyst with eMarketer, commented that becoming involved in "consumers’ conversations" continues to be hard for promoters.

Furthermore, she commented: "Social networking websites are still trying to figure out what sort of advertising works."

Earlier this week, research published by reputation management agency Rapleaf and reported by BusinessWeek revealed that women are using social networking websites considerably more than men.

Because of this, it predicted that the majority of innovations made for the platform in the future will target women.