The incident happened in Paradise Road near Studley Road just before 3.20pm today (March 4).
Officers and London Ambulance Service crews attended and found a boy who had been shot.
He was pronounced dead at the scene shortly after.
Police are working at pace to identify the teenager and contact his next of kin.
Superintendent Gabriel Cameron, who is leading the local policing response, said: “This is an enormously shocking incident which I imagine will cause huge distress to the local community.
“Our thoughts are with the young boy’s family at this devastating time.
“Local officers are on the scene gathering CCTV and speaking to witnesses to piece together what has happened. They will be supported by specialist homicide investigators shortly.
“Please rest assured we will work around the clock to identify and find those responsible.”
No arrests have been made at this early stage of the investigation.
A crime scene and cordons remain in place while emergency services undertake their enquiries, which are ongoing.
If you were a witness or have any information, please call police on 101 with the reference 4116/4MAR.
You can also contact the independent charity Crimestoppers on 0800 555 if you want to remain anonymous.
A spokesperson for London Ambulance Service said: “We were called at 2.32pm today (Tuesday 4 March) to reports of a shooting on Paradise Road, SW4.
“We sent a number of resources to the scene, including an ambulance crew, a paramedic in a fast response car, a paramedic from our tactical response unit and an incident response officer.
“We also dispatched London’s Air Ambulance.
“Very sadly, despite the best efforts of our crews, a person was pronounced dead at the scene.”
