Twitter struggled to grow its user base in 2015 Photo: Dominic Lipinski/PA Wire

Twitter has been racked by a fresh wave of senior departures, with shares in the troubled social network falling heavily yet again despite its chief executive Jack Dorsey attempting to reassure staff. Five executives, including Twitter’s head of media Katie Stanton and Jason Toff, the head of its video service Vine, are leaving the company, some after half a decade of service. It is the latest in a long line of departures at the social network, which is suffering as it struggles to keep up with rival social networks such as Facebook and Instagram. Shares have fallen by 26pc since the start of the year and 35pc since Mr Dorsey, who co-founded Twitter a decade ago, returned as chief executive. They dropped another 4pc on Monday after news of the departures was confirmed. Ms Stanton, who is credited with turning Twitter into a global business by opening its first international offices, said she wanted to spend more time with her family, while Mr Toff is joining Google to work on virtual reality.
5½ years, 600,000+ miles, 20+ countries & many friends. Un grand merci, Twitter, for the adventure of a lifetime— Katie Jacobs Stanton (@KatieS)
January 25, 2016

Personal update! I’m joining Google to work on VR. So much exciting potential there.— Jason Toff (@jasontoff)
January 25, 2016
The other departures are Alex Roetter, Twitter’s head of engineering; Kevin Weil, its head of product; and Skip Schipper, its HR chief. “I’m personally grateful to each of them for everything they’ve contributed to Twitter and our purpose in the world,” Dorsey wrote on Twitter.
Was really hoping to talk to Twitter employees about this later this week, but want to set the record straight now:— Jack (@jack)
January 25, 2016
He said that other Twitter executives would be taking additional responsibility, and that Mr Dorsey himself would be working “day and night” to improve Twitter. The pledge comes despite Mr Dorsey also running Square, a mobile payments company he founded that floated last year. Twitter has gained popularity among celebrities, sports stars and politicians, who can use the service to broadcast short messages to millions of people. However, growth has slowed to a halt at just over 300m users, compared to 1.5bn for Facebook. The company is trying several initiatives to encourage novice users to join such as Moments, a feature that shows popular tweets around a topic, and is considering dropping the 140-character limit on tweets that has defined it for 10 years – a move that risks irritating its loyal users. Many people believe Twitter’s recent share price fall could make it a takeover target, with Google often mentioned as a candidate. Rupert Murdoch’s News Corporation denied it was interested last week. Tech giants’ market caps compared [embedded content]