In the six and a half years that Dick Costolo led Twitter’s executive ranks, he helped grow the company from a few hundred employees to a few thousand. Seven months after leaving Twitter, Mr. Costolo is going small again.
On Tuesday, Mr. Costolo said he plans to build a new start-up focused on physical fitness, one of his longtime passions. The former Twitter chief executive said he would work with Bryan Oki, a health and wellness trainer.
In addition, Mr. Costolo said he will join Index Ventures, the venture capital firm based in San Francisco and London. As a venture partner with Index, he will invest in new companies, as well as advise and mentor entrepreneurs and tech executives.
“Having the opportunity to work with the great team at Index while also embarking on my own new venture makes the beginning of 2016 a very special time for me,” Mr. Costolo said. “I can’t wait to dive in.”
The moves is the next chapter for Mr. Costolo, who announced he was stepping down as Twitter’s chief executive last June as user growth at the social networking company stalled. At the time, Mr. Costolo said little about what he would do after Twitter. Since then, he has acted as a consultant for the HBO series “Silicon Valley,” and spent time advising the show’s writers last year.
Mr. Costolo is no stranger to start-ups. He co-founded a handful of them in the 1990s and 2000s, the most noteworthy being Feedburner, which Google acquired in 2007 for a reported $100 million.
Mr. Costolo joined Twitter after Google, becoming chief operating officer before ascending to chief executive in 2010. He was largely credited with building up Twitter from roughly 300 employees to more than 3,000, and took the company public.
When Twitter’s user growth problems brought scrutiny from Wall Street and others, Mr. Costolo found solace in his fitness regimen, which consisted of everything from CrossFit workouts to bike sprints to weight training.
In his new start-up, Mr. Costolo will work with Mr. Oki on a software platform to help motivate people to work out without focusing on one specific type of fitness community — like yoga or SoulCycle, for instance.
“The fitness industry is transitioning to a world of specialized studios and programs with a multitude of connected devices and software trackers,” Mr. Costolo said. “We’ve developed a system that works within this evolving landscape, and we believe we can scale this system with technology and deliver it to a massive audience.”