The missing boater is identified as 56-year-old Vincent Tangorra of Bethpage.
A search by sea and air began Friday when a personal watercraft was spotted adrift and the Coast Guard was able to contact the brother of its registered owner.
The brother told authorities Tangorra was using his 37-foot sailboat Polaris to tow the watercraft to North Carolina. He said he last spoke with Tangorra on Thursday, when he was told the boat was having engine trouble.
The Coast Guard used the boater's last cellphone location to find the Polaris about nine miles offshore from Avalon.
The Coast Guard said the helicopter search would continue into early Saturday afternoon.