I think this is called "buzz marketing."

quote:

Buzz marketing is a viral marketing technique that attempts to make each encounter with a consumer appear to be a unique, spontaneous personal exchange of information instead of a calculated marketing pitch choreographed by a professional advertiser. . . . Although buzz marketing is not new, Internet technology has changed the way it’s being used. Buzz campaigns are now being initiated in chat rooms, where marketing representatives assume an identity appropriate to their target audience and pitch their product. [Quoted from the link below.]

http://searchcrm.techtarget.com/sDefinition/0,,sid11_gci939341,00.html