Even in Manhattan, abandoned buildings can still be found. Jake Dobkin took some photos of an abandoned school in Harlem.
This building looked like it had been empty for twenty years. Trees were growing out of the floors and poking out of dozens of holes in the roof. All the windows were gone, and the floors that weren't covered with snow were thick with dust and the skeletons of dead pigeons. There wasn't any evidence of human habitation -- no footprints, homeless encampments, or graffiti.
He also found an abandoned ballroom, also in Harlem.
Update: Whoops, looks like Bluejake got swamped. I removed the links so the server can recover...here are the photos on Flickr instead.