Dorsey, who stepped in as interim CEO on July 1, has been candid about the problems faced by the microblogging website . “Investing in @twitter’s future,” Dorsey tweeted on Monday, after disclosing he had bought 31,627 shares, worth about $875,000 at $27.67 per share. Dorsey now owns about 21.9 million shares, or about 3 percent of Twitter.