Twitter's COO, Dick Costolo, is stepping up to take on the role of CEO. He joined Twitter in September 2009, and has taken the lead on Twitter's advertising deals: he's the one who announced "Promoted Tweets" and "Promoted Trends" last spring.
Costolo also has plenty of experience running fast-growing companies: he was most recently CEO of FeedBurner, which he sold to Google in 2007.
Evan Williams, who had been CEO for years, is stepping back to focus on product strategy. Just last week I interviewed Williams about the huge demand for Twitter ads, and the company's challenge of making sure infrastructure keeps pace with traffic on the site. You can watch my interview here.
That fast growth of traffic and advertiser demand is what prompted the CEO swap. In a blog on Twitter.com Williams paints a picture of a company exploding: from 20 employees two years ago to 300 today, from 1.25 million Tweets a day to the average of 90 million Tweets today. And now the company has more than 160 million registered users, up from just 3 million. The company's popularity has grown so quickly outages are not uncommon — many visiting the site this afternoon were met with the all too familiar "Fail Whale."