Twitter Chief Executive Jack Dorsey announced the departure of four of the social-media site’s top executives late Sunday. Media head Katie Jacobs Stanton, product head Kevin Weil, engineering chief Alex Roetter, and HR head Brian Schipper will all leave the company, Dorsey tweeted. The shakeup—the biggest since Dorsey’s return as CEO last year—comes as the company struggles to revive its growth. The company’s stock has fallen nearly 50 percent and now trades below its IPO price on concerns that Twitter has failed to continue to grow its user base. Chief Technology Officer Adam Messinger will head up engineering and product while Chief Operating Officer Adam Bain will handle additional responsibilities on an interim basis. The head of Twitter’s Vine team, Jason Toff, also announced Sunday he was leaving the company, to join Google.