According to the Coast Guard, the surfer went missing around 5:30 p.m. Friday after the surfer's strings became entangled with a nearby motorboat and went underwater near Horseshoe Cove in Gateway National Park.
A boater in the area reported seeing the surfer, a man in his 20s or 30s, go down.
The boater says he saw an unconscious man attached to a kite in harness, but as he was trying to pull the surfer from the water, a gust of wind pulled the kite line from his hands and he lost sight of the man.
In addition to the NYPD and Coast Guard, first-responders from Monmouth County and Atlantic Highlands are assisting in the search.
A popular barrier spit, Sandy Hook is known to attract kiteboarders and surfers from all over.
People who live nearby say they saw nearly a dozen kite surfers on the water Friday.
In the sport, riders use surfboards and large kites to propel themselves across the water.
(The Associated Press contributed to this report.)