Twitter Inc. is losing another co-founder.
Biz Stone, who helped launch the microblogging service in 2006, is leaving day-to-day work at the company, he said Tuesday. Although he will remain involved with Twitter, most of his time will be spent on the relaunch of the start-up where Twitter was first developed: the Obvious Corporation.
The departure marks the latest shift among the executive ranks at Twitter. Jack Dorsey, who came up with the idea for the microblog, returned in March as product chief, two years after being replaced as chief executive by the third co-founder, Ev Williams. Mr. Williams stepped down as CEO in October and was replaced by current CEO Dick Costolo.
Over the past few years Stone has taken on the role of Twitter's evangelist, going on television talks shows to promote the service.
The changes have come as Twitter tries to develop its advertising business and aims to make its service more useful for mainstream users. A study in June found that 13% of adults in the U.S. use Twitter -- a number that is growing but still lags behind the percentage of people who use other popular Web tools, like Facebook.
Mr. Stone said that as Twitter has grown, it has become clear to him that his time could be better spent elsewhere.
"It has come to my attention that the Twitter crew and its leadership team have grown incredibly productive," he said in a post on his blog.
"I've decided that the most effective use of my time is to get out of the way until I'm called upon to be of some specific use."
"We're excited for Ev, Jason and Biz, and look forward to seeing what they create as they return to their entrepreneurial roots with Obvious," a Twitter spokesman said. "Twitter is lucky to have all three of our founders still deeply connected to the company."
Mr. Stone said he would be relaunching Obvious with Mr. Williams and Jason Goldman, who resigned as Twitter's product chief late last year.
In March, Internet company AOL Inc. said it was bringing in Mr. Stone as a "social impact" strategic advisor for the company, as part of its broader integration with news site Huffington Post.
Jennifer Valentino-Devries is a reporter for The Wall Street Journal, where this story originally appeared. Write to her here.