One of top Twitter executives, Ali Rowghani, resigned as chief operating officer yesterday amid a dispute with Chief Executive Dick Costolo.The sudden resignation of Rowghani comes at a particularly thorny time in the company's young history as a public company.

Twitter's stock has fallen about 42 pc this year amid mounting concerns the company's user base is stalling after years of strong growth, The Wall Street Journal reported. 

Also hours after Rowghani's departure, another veteran executive announced on Twitter her own plans to leave the company. Chloe Sladden, head of North American media, was in charge of aligning the social-media company with television.