Video shows a 70-year-old man at a store counter in East Harlem.
A thief lunged inside and grabbed the chain around the victim's neck.
The suspect pulled the man outside.
Police say the chain broke and the thief ran off with it.
It happened on August 24t, about 20 minutes after noon, at a store on Second Avenue.
The suspect is described as black male, ages 16 to 19, wearing a white T-shirt, tan cargo shorts, a black and purple hat and black sneakers.
Anyone with information in regards to this incident is asked to call the NYPD's Crime Stoppers Hotline at 800-577-TIPS.