With marketing and advertising activity in the social-networking sector heating up, the popular online social network for high school and college students Facebook.com - which has recently put itself up for sale - has turned down a $750 million offer, holding out for as much as $2 billion, reports BusinessWeek (via MediaBuyerPlanner). MySpace is the largest social-networking site - with 23.5 billion logged pageviews in February, second only to Yahoo, Media Life writes. Last month, two-year-old Facebook had the seventh-heaviest traffic levels, with 5.5 billion pageviews.

Networking sites are promising new marketing, communication and entertainment channels for reaching millions of younger Americans and teens around the world. With currently low advertising rates, they are attracting marketers of consumer goods and music. Some marketers, however, are hesitant to advertise on them because of potential unwelcome connection between racy or offensive content and the ads running adjacent to it.

But users go the sites to socialize and end up ignoring banner ads, making the ads ineffective on social network sites, writes Jason Calacanis, CEO of the blogging network Weblogs, Inc., on his blog. How do you market to folks at a party? "The answer, in my mind, is that you throw the party," Calacanis writes.