People living in the Leigh area who travelled along the M61 towards Preston on Monday morning are being asked for help.
For police believe a man could hold vital clues to the death of the young man who was knocked down and killed on the motorway.
Kane Fairbrother, 16, from Horwich, was in collision with a lorry near Bolton West services and died at the scene.
Motorists who use the route are being asked if they saw a man in a grey tracksuit in the area at the time of the accident at 9.50am on Monday.
Insp Damian Kitchen from Lancashire Police Force Roads Policing Unit said: “This is an extremely tragic incident and our thoughts go out to the young man’s family and friends.”
Anyone with any information about the acccident is asked to ring police on 08451 253545.