London Twitter said it would start featuring ads as part of the company's effort to turn its popularity into profit.
Twitter co-founder Biz Stone unveiled the new advertising platform, called Promoted Tweets.
Tweets paid for by Twitter's advertising partners will now be displayed at the top of the search results page.
Companies that will feature ads on the site include Best Buy, Starbucks and Sony Pictures.
Other than carrying a label that signals they are being paid for by an advertiser, the promoted posts will look like a regular tweet.