It happened around 11:30 p.m. on Friday at Regal Brandywine Town Center.
Troopers released photos of the suspect on Thursday.
Officials say the suspect, who allegedly had a gun, approached the victim and demanded cash.
When the victim initially refused, the suspect then forcefully took the victim's money before fleeing the area, according to troopers.
The victim was not injured.
Detectives are asking anyone with information relevant to the investigation to contact Detective D. Armstrong at (302) 365-8440. Information may also be provided by sending a private Facebook message to the Delaware State Police or contacting Delaware Crime Stoppers at 1-800-847-3333.