Dick Costolo speaks on June 20, 2012, during an event...

Dick Costolo speaks on June 20, 2012, during an event at the International Advertising Festival in Cannes, France. The company announced June 11, 2015 that he is stepping down as CEO on July 1. Credit: AP

Dick Costolo will step down as CEO of Twitter after almost five years, the company announced Thursday in a news release. It did not disclose a reason for his departure.

As Twitter Inc. announced the move, Costolo also tweeted the news through his own account.

The San Francisco company says co-founder and chairman Jack Dorsey, 38, will be its interim CEO while it looks for a replacement.

Costolo, 51, will stay on Twitter's board of directors. He has been a director since September 2009 and became CEO in October 2010.

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