Sussex Police has issued an urgent appeal for witnesses to the collision in East Preston on Tuesday (August 31).
A green Kawasaki J300 was travelling southbound on Station Road at around 7.10am when it left the road at the junction with Vicarage Lane and hit street furniture.
The rider has been identified as a local 15-year-old boy and his next of kin have been informed, police said.
Detective Sergeant Rob Baldwin of the Serious Collision Investigation Unit, said: “This is a tragic incident involving a child and we are conducting a thorough investigation to establish the circumstances.
“I would appeal to anyone with information, who has not yet been spoken to by police, to contact us as soon as possible.
“We are particularly interested in dash camera footage or CCTV showing a green and silver motor scooter being ridden around the local area prior to the collision.”
Anyone with information is asked to call 101 or email [email protected], quoting Operation Hawthorns.