Twitter is reportedly planning a new advertising model that will serve targeted adverts via searches on the social network.

A story in the Wall Street Journal’s AllThingsD blog suggests that the new model will be similar to Google’s PPC search engine marketing platform, AdWords. According to the WSJ report, “a search for, say, ‘laptop’, may generate an ad for Dell”.

These adverts won’t appear directly in the user-specific feeds – otherwise known as a “twitterstream” - but will be limited to searches made internally on the social network service. Adverts will be in the same format for content generation as all posts on Twitter – in text messages of 140 characters or less.

The WSJ story also suggests that whilst initially Twitter will work with “ad agencies and buyers to seed the program”, the company plans on “moving to a self-serve model like Google’s, down the road”.

Currently, advertising is limited to a tiny, low profile text box in the top right section of a Twitter user’s homepage. The rumoured system would help the social networking company generate long-term revenue from its estimated 75m users, as the idea of charging for use of the service appears to have been discarded.

Whilst deals with major search engines in 2009 led to the company posting a profit for the first time, the future of Twitter as a viable business has long been in doubt despite the massive popularity of the service. Although Bing and Google now include Twitter posts in their ‘real time search’ results, it is doubtful that the proposed system would serve ads directly into this feed.

Although the keyword-targeting would make it feasible it would likely be extremely unpopular with both the search engines, as it would compound the problem of Twitter messages being used as a means of advertising in search results without paying additional revenue.