The New York Post said Leiby Kletzky, 9, was last seen Monday leaving the Boyan Day Camp in Brooklyn at 4:50 p.m. He was supposed to meet his mother eight blocks away but didn't show up.
Assemblyman Dov Hikind, D-Brooklyn, said volunteers spent all night searching yards and anywhere the child could be.
The Post said buses with New Jersey volunteers have come to help with the search.
Jacob Daskal, a member of the Shomrim volunteer civilian patrol, told the Post, "It might be an abduction, but we're still hoping it's not."
Daskal said a surveillance camera showed the boy leaving the day camp, but the New York Daily News said there were conflicting reports on whether the boy was caught by the camera.
A Shomrim official said the family confirmed the boy walked by himself, but normally he took the bus.
Hikind's office, the boy's family and friends are offering a $100,000 reward for any information on his whereabouts, the newspaper said.
The Daily News said Leiby is about 4 feet tall, weighs 50 pounds and was last seen wearing a blue shirt with green and white stripes, blue pants, black leather belt, black socks, black sneakers and a "Nechmod Day Camp" knapsack.