The incident occurred at the 7/11 store on Grand Avenue in Baldwin at around 11:40 p.m. Sunday, Oct. 9, according to Nassau County police.
Investigators said the suspect walked into the store with his hand under his shirt, gesturing that he had a gun.
He then got into the cash register and stole and undisclosed amount of money before leaving on foot, police said.
There were no reports of injuries following the robbery.
Police described the suspect as an adult male who was wearing a black baseball cap, dark sunglasses, gray sweatshirt, and dark pants with black boots.
Anyone with information is asked to contact Nassau County Crime Stoppers at 1-800-244-TIPS. All callers will remain anonymous.
Click here to follow Daily Voice Massapequa and receive free news updates.