“We don’t see how the departure of the heads of three major business divisions can be viewed as a positive in the middle of an attempted business turnaround,” Stifel analysts wrote in a note. The brokerage downgraded the stock to “hold” from “buy.”

Twitter shares closed down 4.6%, at $17.02 on the New York Stock Exchange. They have plunged 67% since April.The microblogging service’s user base has stubbornly remained just above the 300 million mark for the past year, in part because new users are having trouble figuring out how to use the site.
Dorsey said in July it is “not clear why they should use Twitter.” He has urged more disciplined execution and a simpler service.

He is also battling concerns that Twitter has not defined its role in the burgeoning social media landscape. Some regard it is a media and news service, while others say it is to connect with celebrities or follow live events.

The executives leaving the company are media head Katie Jacobs Stanton, product head Kevin Weil, head of engineering Alex Roetter and human resources head Brian “Skip” Schipper, according to a tweet by Dorsey on Sunday night.

Weil will not be replaced and Adam Messinger, chief technology officer, will oversee all engineering and consumer product, design and research, user services and the development platform, called Fabric, according to a Twitter spokesperson.

Dorsey, sometimes heralded as a product visionary, has taken more control over product development since returning to the helm.

Jason Toff, who heads Twitter’s video streaming service Vine, also tweeted that he was leaving Twitter to join Google to work on virtual reality, but Dorsey’s tweets – which included a screenshot of text commending the executives on their time at the company – did not mention him.

The departures of Weil, Stanton and Roetter were noteworthy because all three had been at the company for more than five years, meaning most of former CEO Dick Costolo’s management team is now gone.

Dorsey, who became interim CEO in July and then CEO in October, has called for “bold rethinking,” but has not yet clarified what that means.