While the rapid growth and young audience of social networks like MySpace and Facebook are attractive to marketers, advertisers and analysts still question whether social networks can last and break into mainstream marketing, writes the New York Post (via MediaBuyerPlanner). The trick of advertising on social networks seems to be creating less formal and invasive advertising techniques that attract young users.

"This is a new type of advertising that they're still getting used to," said Janne Kouri, of Sulake Corp. - parent of Habbo Hotel online chat site.

Advertisers are having a hard time dealing with the new and unpredictable nature of social networks - which may contain risqué content, and have allegedly been used by predators in recent abductions and murders.

"What they struggle with is the content, the environment and the right approach - pretty much everything," said Jeff Lanctot, VP of media for Avenue A-Razorfish, the largest buyer of internet ads.

Research firm PQ Media estimated that ad spending on "user-generated media" totaled $20.4 million last year, but will grow to a possible $49.8 million this year - a conservative estimate as Rich Greenfield, of Pali Research, estimated that MySpace alone racked up $13 million in ads last month.