BEIJING — Guo Chuan, an oceangoing Chinese adventurer, set off on a trimaran from San Francisco last week, hoping to establish his latest sailing record with a 20-day sprint to Shanghai.

But on Thursday, the American Coast Guard said it had found Mr. Guo’s 97-foot, red-hulled boat drifting and unmanned in the Pacific Ocean almost halfway to his destination. His life jacket was still onboard.

Officially, Mr. Guo remains missing. But the Coast Guard said it had suspended its search and offered commiserations to his family.

Mr. Guo “was a professional mariner with a deep passion for sailing,” Capt. Robert Hendrickson, the chief of response for the Coast Guard’s 14th District, which oversaw the search, said by email.