Despite all the recent problems Facebook is having over privacy concerns, Bloomberg's Business Week reports that the social networking site saw a four-fold increase in the number of advertisers using the site since the start of 2009.

Facebook has been opening offices around the world to serve its growing base of advertising clients who are targeting the growing base of users - now said to be more than 500 million. According to figures fro comScore, Facebook ran 176 billion display ads in the US in the first quarter of 2010, up from 70.7 billion a year earlier.

The advertising options available allow for targeted campaigns which have led to some of the privacy concerns by users who feel that too much information is being made available. Facebook sells ads on either a CPM (cost per thousand impressions) or CPC (cost per click) basis, with them being placed on the home pages of users, where the latest comments, pictures and links from their friends are posted. The ads also show up next to profile pages, which may include a person’s information such as gender or birth date.