The attack happened at Tao Spa Bodywork in Flushing just before 11 p.m. on Thursday.
Police say the customer threatened an employee with a hammer over a refund and dragged her into the waiting room.
Three other employees tried to calm him down, but the attacker allegedly choked one of them and threw her against the wall.
The employees gave him $40 so he would leave, but on his way out, he reportedly smashed open a piggy bank and stole the money.
All of the victims were treated at the scene and are expected to be OK.
The suspect is described as 20 to 30 years old, 5 feet 6 inches and 160 pounds with black hair. He was last seen wearing a gray hooded coat, dark jeans, tan work boots and a light-colored backpack.
Anyone with information is asked to call Crime Stoppers at 1-800-577-TIPS (8477).
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