Detectives in Franklin said a man came into the Twice Daily Shell gas station at Royal Oaks Boulevard and Oak Meadow Drive and threatened the clerk with a box cutter, demanding the clerk give him money.
The incident happened just after midnight Saturday morning.
But when the clerk apparently didn't move fast enough for the robber, the suspect took the entire cash register and bolted out the front door.
Police said the man likely had a getaway vehicle waiting nearby.
Police said the armed robbery suspect was still on the loose as police were in the area continuing to investigate Saturday.
Police described the suspect as a white man, about 5'6'' tall, weighing around 150 pounds. He was wearing a gray hoodie and had a long, skinny face, dirty blonde hair, and a reddish brown goatee.
Franklin Police said they're offering up to a $1,000 reward for information that can lead to the arrest of the person in the surveillance image. Anyone with information has been urged to call Franklin Crime Stoppers at 615-794-4000.