It happened last Friday at 1:47 p.m. inside a McDonalds on 82 Street in Elmhurst.
The girl and her mother were walking up the stairs when the man followed them, and then took the chain from her neck.
The suspect then ran away. No one was injured.
The suspect is described as approximately 40 years old, balding, and wearing a grey button down shirt and blue jeans.
Anyone with information in regards to this incident is asked to call the NYPD's Crime Stoppers Hotline at 800-577-TIPS.