The incident happened along Bristol Pike in Morrisville on Wednesday afternoon.
The man reportedly got out of his tan pickup truck and accosted the teen, who ran away.
Police describe the man as 'light-skinned,' standing about six feet tall. He is in his 40s or 50s with a large build and scruffy facial hair.
Anyone with information is asked to contact the Falls Township Police Department at 215-945-3100.