Twitter Inc. chief executive officer Dick Costolo abruptly announced he was stepping down yesterday amid increasing scrutiny of the company’s slow user growth and inability to attract advertisers at the same rate as its competitors.

Costolo will be replaced by co-founder Jack Dorsey on an interim basis.

According to a source familiar with the matter, it was Costolo’s decision to leave, and Costolo said he brought it up with the board last year as it began talking about succession planning.

Twitter has had a number of shake-ups in its management. Co-founders Jack Dorsey and Evan Williams both served as CEOs of the company before Costolo, and Costolo has overhauled much of his management team over the past year.

“Unfortunately this news isn’t surprising,” said Nate Elliott of management consultant Forrester Research. “The bottom line is that Twitter isn’t very good right now at serving either its users or its marketers.”

Costolo will step down on July 1 and will continue to serve on the board, the company said in a regulatory filing.

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