The incident occurred in Clun Road, Littlehampton, at 2.30pm on Friday, July 22.
The boy, wearing a blue t-shirt, was walking his bicycle across the road from Egan Way towards Wickbourne Stores when he and the car were in collision.
The boy was knocked to the ground, sustaining cuts and bruises for which he was treated at Worthing Hospital but not detained.
The car, believed to be a grey Nissan Qashqai or similar, failed to stop. It continued south-east along Clun Road towards Wick Farm Road.
Anyone who saw the collision occur or who knows the driver or vehicle involved is asked to email [email protected] or phone 101, quoting serial 899 of 22/07.