Twitter chief executive Dick Costolo in surprise departure from firm

Twitter boss Dick Costolo will quit the social media giant on 1 July, to be replaced in the interim by chairman and co-founder Jack Dorsey.

The company has set up a company to find a permanent chief executive.

"I am deeply appreciative of the confidence the board, the management team and the employees have placed in me over the years, and I look forward to supporting Twitter however I can going forward," Costolo said in a statement.

"I am tremendously proud of the Twitter team and all that the team has accomplished together during my six years with the company," he added.

"We have great leaders who work well together and a clear strategy that informs our objectives and priorities."

Twitter has faced mounting pressure from investors as growth appeared to stall. There have been a number of executive changes, too, that have unsettled the firm.

In April, the firm missed Wall Street's forecasts for revenue growth and posted a net loss of $162m (£104m).

Reuters reported that Twitter is lagging behind other social media companies, such as Facebook, Instagram and Snapchat in its bid to gain new users.

Data firm eMarketer forecast that Twitter's monthly user base will grow only at 14.1% this year, compared with more than 30% two years ago

Following the announcement that Costolo was stepping aside, Twitter shares jumped by more than 7% in trading after Wall Street had closed.

Costolo will continue to serve on the board, Twitter said in a regulatory filing, and he has agreed to cancel all of his remaining unvested equity in Twitter after he steps down.