The latest incident happened around 5 p.m. at a GameStop store in Mattituck.
Police say the suspect may have been banking on a lot of cash being on hand due to the overnight released of the latest Call of Duty game.
He fled with under $1,000 in a jeep that has been seen at other robberies connected to the suspect.
No injuries were reported.
Police say that over the past two weeks, the man has entered eight other establishments and pretended to purchase an item.
When the employee opens the cash register, the man displays a black handgun and demands cash.
The suspect then flees the location.
The other robberies occurred at seven gas stations located in Eastport, Calverton, Mastic, North Babylon, St. James, Dix Hills and Bohemia, as well as at Jamba Juice in Stony Brook. No one was injured during any of the robberies.
The suspect is described as a white man, between 25 and 35 years old, approximately 5-foot-10 to 6-foot-2 with a thin to medium build. He usually wears a dark-colored or gray hooded sweatshirt.
Detectives are asking anyone with information on these robberies or if anyone recognizes the suspect in the attached photo to call Crime Stoppers at 1-800-220-TIPS. All calls will be kept confidential.