It happened before 1:30 p.m. Friday at Concord High School in the 2500 block of Ebright Road.
Authorities say prom tickets were being sold in the hallway when a boy, later identified as a 16-year-old student at the school, grabbed the cash box and ran off.
State police were still looking for the boy on Monday.
The school's prom is scheduled for May 30th.
