The robbery happened at Jake's Hamburgers on Kirkwood Highway in Elsmere, Delaware shortly before 9:00 p.m. Wednesday.
Police say the suspects ordered the manager on duty to empty a safe and hide under her desk.
Two other employees and two customers were also ordered to lie face down on the ground.
The thieves then tied them up and fled.
"It's an unfortunate sign of the times, you know? Times are tough and people are getting very desperate," said District Manager Andre Schleiniger. "It sickens me a little bit that we work so hard for everything that we have and someone feels the right to come in and just take it."
It is not clear how much money the robbers got away with.
No one was hurt.