A frantic, full-scale search kicked into high gear Tuesday for a missing boy who disappeared after leaving a Brooklyn day camp. Leibby Kletzky, 9, was last seen at his school, Yeshiva Boyan in Borough Park, around 5 p.m. Monday after coming back from a field trip, cops said. The Orthodox Jewish boy was supposed to meet his mother soon after but never showed up. There were conflicting reports that a surveillance camera captured images of the boy walking at the corner of 13th Ave. and 50th St. Volunteers have scoured the neighborhood since, but the boy remains missing. "Right now,...