Dorsey gets Twitter CEO post, Bain appointed COO

Dorsey is also CEO of mobile payments company Square, creating the unusual situation of having one person lead two high-profile Silicon Valley companies at the same time. He's also on the board of The Walt Disney Company.

Dorsey has been Twitter's interim CEO since Dick Costolo stepped down abruptly four months ago, so the big change, approved by the board on September 30 according to an SEC filing, is to make Dorsey's role permanent. That filling also said that "there are currently no plans to provide Mr. Dorsey with direct compensation for his role as Chief Executive Officer."

The board also appointed Adam Bain, who has been president, Global Revenue & Partnerships since September 2010, as COO. Also on September 30, Costolo resigned his position on Twitter's board. While Dorsey had been Twitter's chairman, the SEC filing made public on Monday said that he will no longer serve in that role although he will remain on the board. It did not say who will take on that position.

Dorsey's main tasks at Twitter are to figure out how to attract users at a faster pace, and to create a path to profitability.

The social network is under intense pressure to figure out how to draw new users to its service. Unlike Facebook, which ramped easily to a billion subscribers, Twitter grew quickly at the start but seems to have hit a plateau.

It reported strong growth in its advertising business last quarter, but the social network isn't profitable, in part because it's investing in the infrastructure that delivers its service.

More worryingly, the number of core users who access Twitter at least once a month increased by only 2 million last quarter, to 304 million.

"This is unacceptable and we’re not happy about it," Dorsey said at the time.

In July, he outlined steps to draw more users, including making it easier for people to get started on Twitter, and showing more meaningful tweets in timelines.

"People all over the world know of the power of Twitter, but it's not clear why they should harness it themselves," he said then. Twitter needs to communicate better why people should want to use it.

He even talked about rethinking Twitter's signature chronological tweet stream, but a challenge for the company is that any big changes could alienate its core base.

Dorsey created Twitter in 2005 and 2006 with Evan Williams, Biz Stone and Noah Glass. Dorsey became CEO soon after but lost the role in 2008, because he became a "distracted manager," according to a profile in The New Yorker.

The following year he co-founded Square, known for its technology that lets small merchants take credit card payments on smartphones and tablets. He's chairman and CEO of that company, in addition to now being CEO of Twitter.

Twitter's investors don't seem thrilled at having a CEO who divides his time between two companies. The company's stock slipped more than 8 percent last week after reports emerged that Dorsey was likely to get the top job.