18-year-old Ariel Manuel Martinez-Colon was last seen at approximately 12:30 a.m. Sunday.
Police say Ariel and his family were traveling on the Schuylkill Expressway when he asked for the car to pull over.
Once the car pulled over near the South Street Bridge, police say Ariel got out and ran away.
His family was unable to catch up to him.
Police say Ariel suffers from schizophrenia and depression and may not be taking his medication.
He only speaks Spanish and resides in Lancaster, Pa.
Ariel Manuel Martinez-Colon is described as an 18-year-old Hispanic male, 145 pounds, with a light complexion, short black hair, brown eyes, thin mustache, beard, and long chin hair.
He was last seen wearing a black hoodie with white design on the front, dark blue jeans, and an Adidas baseball hat.
Anyone with information on Ariel's whereabouts should contact South Detective Division at 215-686-3013/3014 or call 911.