Next Twitter boss faces complex challenges, says departing Dick Costolo

In interview before his last day in job, CEO says going public accelerated short-term-thinking, and regulation would pose threat to free speech

The outgoing chief executive of Twitter has said he underestimated the pressures that going public would place on the company and warned that his successor would nevertheless have to manage an increasingly complex set of geopolitical challenges as well as the demands of Wall Street.

Speaking to the Guardian before his last day at the company on Wednesday, Dick Costolo said that while Twitter had grown revenue by 97% year on year to $1.7bn (1.1bn), the pressure placed on the company obscured its other achievements in bringing 302 million monthly active users on to the service.