Dick Costolo to step down as chief executive of Twitter Inc. on July 1, as the social media company struggles to convince Wall Street of its growth strategy.

Co-founder Jack Dorsey will serve as interim CEO until a replacement is found. Coastal will, however, remain on the board.

In the official release, Costolo made no mention of reasons for his departure from the company.

Coincidentally, Twitter stock is up 7%. Make of that what you will.