Twitter COO Costolo replaces co-founder as CEO

Twitter co-founder Ev Williams will hand the chief executive job to COO Dick Costolo, who joined the fast-growing microblogging company about one year ago to spearhead its money making efforts.

Williams will focus completely on product strategy effective immediately, he wrote in a post on the Internet company's official blog on Monday.

Costolo joined Twitter as chief operating officer in September 2009 after he sold FeedBurner, an Internet company he had co-founded, to search giant Google Inc in 2007.

Costolo launched Twitter's first efforts at selling ads on its service earlier this year. In an interview with Reuters on Monday, Costolo said the so-called Promoted Tweets and Promoted Trends advertising services were "successful beyond our wildest dreams."

He said that privately held Twitter does not disclose revenue or comment on whether the company is profitable.

Williams said Twitter has more than 165 million registered users, up from just 3 million when he became CEO two years ago. The staff has grown to 300 from 20 over that period, he added.

"Growing big is not success, in itself," Williams wrote. "Success to us means meeting our potential as a profitable company that can retain its culture and user focus while having a positive impact on the world."

He described Twitter's efforts at making money, primarily through advertising, as "early, but successful."

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