The head of Twitter has announced he is stepping down, as the company focuses its energy on making money from its widespread microblogging service.
Evan Williams said he wanted to work on strategy rather than marketing
Evan Williams, a co-founder who has led the San Francisco-based company for the past two years, said he would be working solely on product strategy from now on.
He added that had asked the company's chief operating officer Dick Costolo to take over the helm.
Twitter has seen rapid growth since its creation in 2006, but is yet to announce that it has generate a profit.
"We're making money but we have a long way to go before we're putting money in the bank," Mr Williams' co-founder Biz Stone told Bloomberg in June.
Mr Williams has overseen a recent redesign of Twitter's website to attract new users and give advertisers a better platform to showcase photos or videos.
But as the company has grown to employ 300 people there is "less and less time" for him to focus on strategy, Mr Costolo said.
Writing on the Twitter blog, Mr Williams said: "Building things is my passion, and I’ve never been more excited or optimistic about what we have to build.
"This is why I have decided to ask our COO, Dick Costolo, to become Twitter’s CEO.
Dick Costolo has been leading advertising initiatives since he joined Twitter last year
"During his year at Twitter, he 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."In the two years that Mr Williams has been in charge, Twitter has seen the number of users rise from 3m to 165m.
Yet the rapid expansion has led to frequent technical problems, which sometimes stop users accessing the service or cause problems presenting a user's timeline of tweets.
"The challenges of growing an organization so quickly are numerous," wrote Mr Williams.
"Growing big is not success, in itself. 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."
Twitter's growing popularity has fuelled expectations that marketers could use the messaging service to target ads to consumers interested in real-time information about breaking events and other topics.