The incident happened near Hazelwood Crescent at around 7.20pm today (July 21).
Officers, London Ambulance Service, and an air ambulance attended and found a boy injured.
He was pronounced dead at the scene shortly after.
Police work to identify and inform his next of kin is ongoing.
Six males have been arrested on suspicion of murder and remain in custody.
A spokesperson for Metropolitan Police said: “A murder investigation is under way following a shooting in Ladbroke Grove.
“Police were called at approximately 19:20hrs on Sunday, 21 July to reports of a shooting in a park near Hazlewood Crescent, W10.
“Officers, London Ambulance Service and London’s Air Ambulance all attended the scene.
“A teenager, believed aged 15, was found suffering injuries. Despite the best efforts of the emergency services he was pronounced dead at the scene.
“Work is ongoing to identify and inform his next of kin
“No reports of any other injuries.
“Six males have been arrested on suspicion of murder and remain in custody.
“A crime scene remains in place at the location.
“Anyone with information at this early stage is asked to call 101 or ‘X’ @MetCC and quote CAD6343/21Jul.
“You can also report information anonymously to the independent charity Crimestoppers on 0800 555 111.”