For many months, Twitter has been trying to reshape itself as a growing social media service. That attempt now includes reshaping the company’s top ranks.
On Wednesday, Twitter said that Adam Bain, its chief operating officer, plans to leave the company. Mr. Bain was well liked by Wall Street for building up and running Twitter’s once fast-growing advertising business.
Many of Mr. Bain’s duties and his direct lieutenants, including those who manage ad sales and partnerships with marketers and broadcast media companies, will be under the purview of Anthony Noto, Twitter’s chief financial officer. Mr. Noto will take on the chief operating officer title, and Twitter said it would begin a search for a new chief financial officer.
“The past six years have been incredible, and I’m inspired by what Twitter has become and what it will be in the future,” Mr. Bain said in a statement. “Anthony and I have worked side by side since he joined Twitter in July 2014 and I have full faith in what he and the teams will accomplish in the future.”
Jack Dorsey, Twitter’s chief executive, added: “Since joining Twitter in 2010, Adam has built an amazing team and a global business from the ground up.”
The changes are more than just the run-of-the-mill executive churn at Twitter, which has seen plenty of departures in the past. Together, they amount to the most significant shake-up under Mr. Dorsey, who was appointed chief executive in October 2015 after an interim stint.
He has been struggling to turn Twitter into a moneymaking enterprise with a growing audience, but his efforts have largely stalled and the company recently flirted with selling itself.
Mr. Bain, 43, had his six-year anniversary at Twitter in August. Over his time at the company, he helped build Twitter’s ad efforts from the ground up, and was once considered a top candidate to be chief executive before Mr. Dorsey got the job.
Inside Twitter, Mr. Bain was seen as a corporate cheerleader who was known for his positivity. Last year, employees circulated a hashtag, #AdamBainIsSoNice, after an article about him appeared online in Recode.
In recent quarters, the growth of Twitter’s ad business has slowed and Mr. Bain has had to grapple with a more challenging digital advertising environment.
Last month, Twitter said it would slash 350 jobs, or about 9 percent of its work force, as part of an attempt to move the company more quickly toward profitability in 2017.
Many of those cuts are focused on restructuring Twitter’s sales and marketing efforts, which were under Mr. Bain.
Mr. Noto, 48, who joined Twitter two years ago as chief financial officer, has been amassing more responsibilities. He has been instrumental in helping to orchestrate and execute Twitter’s plan to be more of a destination for live streaming video, including striking a partnership with the National Football League to stream Thursday night games.
Internally, Mr. Noto is popular, frequently appearing onstage at companywide meetings cheering on Twitter’s live-streaming efforts.
Mr. Bain, who is regarded as a top executive prospect and has been approached by a number of companies during his tenure at Twitter, did not disclose his plans.
Current and former Twitter executives describe the relationship among Mr. Bain, Mr. Dorsey and Mr. Noto as amiable.
Three people who work with Mr. Bain, and who requested anonymity because their conversations with him were private, said he would not join a major Twitter competitor like Facebook, a move that other Twitter executives have made in the past. Instead, Mr. Bain will most likely pursue something outside the advertising industry, these people said.