Police say the unknown suspect entered the restaurant in White Township, about 45 miles northeast of Pittsburgh, about 9:45 p.m. Sunday.
The ski-masked robber repeatedly asked to speak with the manager, whom the employees couldn't find. In the process of looking for the manager, one of the employees opened a rear door which caused an alarm to go off and scared away the suspect.
Troopers from the Indiana, Pa. barracks couldn't find the suspect when they arrived moments later.
Nobody was hurt by the suspect, who had a gun.