The suspect pulled out a handgun, approached the two workers, and ordered them to take him to the safe.
The workers told the gunman they did not know the combination.
Police say one of the employees gave the gunman $20 of his own money, and the gunman fled.
Police are asking the public for help finding the robber.
He is described as black, 30 years old, 5 feet 8 inches tall and weighing about 170 pounds.
He was wearing a black jacket, black jeans and a gray ski cap with a handkerchief over his face.
Anyone with information is asked to call the LAPD at (213) 473-0154.