The unidentified 25-year-old man was swimming in the Atlantic Ocean with a group at Beach B at about 7:30 p.m. when he was seen in distress, said spokeswoman Daphne Yun.
Lifeguards were off-duty at the time on that beach, but others working at a concert at Lot E responded to the scene, she said.
Also responding were the Coast Guard, New York City Police aviation, the Monmouth County Sheriff’s office, and police and emergency volunteers from Sea Bright, Highlands and Atlantic Highlands, she said.
The water search was called off at about 8:45 p.m. because of darkness, Yun said, and the air operation continued until about 10 p.m. without success, she said.
Yun said she did not have further identification of the swimmer, who remained missing at 10 a.m. Thursday.