The incident happened at the Chevron station on Whittier Boulevard and Greenleaf Avenue around 6:50 a.m.
Authorities said the suspect pulled up to the gas station in a white pickup truck and then managed to attach something to the cash machine without catching the clerk's attention.
"The clerk heard a thump and saw the truck leaving, dragging the ATM," Whittier police Lt. Mike Przybyl said.
The male suspect was last seen heading west on Whittier Boulevard.
It remains unclear just how much money the thief got away with.