Officers say it happened around 3:00PM Thursday, near the Carlisle Pike and PA 581 East bound.
A driver of a white Subaru pointed a sawed off shotgun at the victim and threatened his life.
The suspect is described as a white male.
The white Subaru is either an Outback or a Forrester with a roof rack as well as red and green stickers on the left side window.
It was last seen exiting US 11/15 towards Gettysburg.
Anyone with information is asked to contact State Police.