Since Twitter emerged as a social media phenomenon in 2006, one of the company's persistent issues has been the lack of a business model. That's where Costolo, 46, comes in. The former Google executive and Feedburner CEO was tapped by Twitter last September to head up the social media giant's monetization efforts, which now include the rollout of Promoted Tweets, ads that will appear in search results, user feeds, and third-party Twitter applications like TweetDeck. The company says that more than 10 major advertisers are onboard, including Disney, Starbucks, Virgin America, and Bravo. Will the new ad model fly? Costolo and company promise an update in after the fourth quarter. --J.P.M.
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Last updated July 09 2010: 1:19 PM ET