Dick Costolo, the chief operating officer, will take over from Evan Williams and be charged with leading the micro-blogging service to profitability.
Twitter chief executive Evan Williams stepped down on Monday, handing over the reins to Chief Operating Officer Dick Costolo, who will now lead the company's effort to build a profitable business model.
On the company's blog, Williams said he would leave running the company to Costolo, so he could focus on product development at the micro-blogging site.
"I am most satisfied while pushing product direction," co-founder Williams said. "Building things is my passion, and I've never been more excited or optimistic about what we have to build."
Since taking the job of CEO two years ago, Williams has struggled with the challenges of growing an organization quickly. When he first took over, Twitter was generating about 1.25 million tweets a day, compared to 90 million today. During the same timeframe, the site grew from 3 million registered users to more than 165 million.
"Growing big is not success, in itself," Williams said. "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. This is no small task."
Williams brought in Costolo as COO about a year ago to help with managing Twitter. During that time, Costolo has been "a critical leader in devising and executing our revenue efforts, while simultaneously and effectively making the trains run on time in the office," Williams said.
Costolo has been instrumental in moving Twitter toward profitability through an advertising program launched in April called Promoted Tweets. The ads, which are supposed to be relevant to search queries on Twitter.com, are placed at the top of results pages.
The company started the program initially with a select group of advertising partners: Best Buy, Bravo, Red Bull, Sony Pictures, Starbucks and Virgin America. Twitter expected to add advertisers to the trial and later open Promoted Tweets to other advertisers and to Twitter partners, such as makers of Twitter clients.
In June, Twitter rolled out an extension of Promoted Tweets called Promoted Trends, which is a topic that is already a Twitter trend, but one that is not yet popular enough to have arrived on the Trending Topics list. Twitter is in the process of tuning its application programming interface to give developers access to the two ad mechanisms.
Last month, Costolo spoke at ExactTarget's Connections '10 user conference in support of the latter company's Interactive Marketing Hub that's designed to allow marketers to power all forms of real-time interactive marketing across email, social media networks, such as Twitter and Facebook; mobile devices and websites. Costolo's addressed more than 2,000 marketers at the show.
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