The incident happened on Kilbowie Road, in the West Dunbartonshire town, at about 07:45.
The 52-year-old male van driver was taken to Glasgow's Queen Elizabeth University Hospital along with the teenager, a 42-year-old man and 48-year-old woman.
The driver has since been discharged but is the subject of a police inquiry.
Police have appealed for witness to the crash to come forward.
It resulted in the closure of the route between the A82 Great Western Road and Second Avenue. All four people injured remain in hospital, police said.
Insp Adam McKenzie of Police Scotland said: "It is quite clearly a serious incident from the word go when pedestrians are struck by vehicles.
"One person had been knocked completely over the small wall at the back of the bus stop.
"The driver was still partially trapped within the vehicle and debris from the bus stop was embedded in the vehicle as well."
He added: "At the moment we are conducting the forensic side of the inquiry - photographs, measurements and every piece of physical evidence that we can gather.
"The vehicle will be removed and will be subject to a full mechanical examination as well.
"It's a busy area and I would ask that if anyone in a vehicle or a pedestrian has witnessed it this morning, and has not already spoken to police, could they please come forward."
Four people, including a 15-year-old boy, have been injured after a van crashed into a bus stop in Clydebank.