Emergency services scrambled to the scene which happened at around 7.30pm last night on the A303 close to the Countess Roundabout towards Stonehenge.
The lad, from London, was pronounced dead at the scene after the black BMW collided with the lorry which was parked in a layby.
The driver of the car, a man in his 40s, and a passenger, a 15-year-old boy, suffered potentially life-changing injuries and were taken to Southampton General Hospital by air ambulances.
The driver of the lorry did not suffer any injuries.
The A303 has been reopened eastbound between the A345 and the A360 near Stonehenge following the fatal crash.
Inspector Will Ayres of the Roads Policing Unit said: “This is a tragic incident where a young boy has lost his life and two more people are in a serious condition in hospital.
“Their next of kin have been informed and are being supported by specially trained officers.
“Our thoughts are with them at this very difficult time.
“I would urge anyone who witnessed anything to please get in touch with us.”
Witnesses to the collision or anyone who may have dash cam footage are urged to contact the serious collision investigation team on 01225 694597 quoting log number 289 of yesterday’s date.
Two air ambulances were scrambled to a road traffic collision on the major A-road that passes Stonehenge, near Amesbury, at around 7.30pm on Saturday evening (9 July).
A black BMW veered off the carriageway and struck the rear of a lorry, which was parked in a lay-by. An 11-year-old boy, from London, was declared dead at the scene by medics.
The driver of the car, a man in his 40s, and a passenger, a 15-year-old boy, both from London, suffered potentially life-changing injuries and have been taken to Southampton General Hospital.
One of the wounded casualties was airlifted to the Major Trauma Centre by Hampshire and Isle of Wight Air Ambulance. Wiltshire Air Ambulance also attended the scene but did not transport anyone.