The victim, believed to be aged 18, was found with a stab injury in Uxbridge Road, Shepherd’s Bush, on Wednesday night.
Cops said officers were called at about 9.20pm, along with paramedics and the London Air Ambulance.
Despite the efforts of medics, the teenager died at the scene a short time later.
A murder investigation has been launched and police are working to track down those involved in the incident.
Detective Inspector Luke Wyllie, from Hammersmith and Fulham police, said: “A young man’s life has been tragically cut short.
“Our thoughts are with his friends and family at this very difficult time. We are doing everything we can to apprehend those involved”
Detective Inspector Luke Wyllie
“Our thoughts are with his friends and family at this very difficult time. We are doing everything we can to apprehend those involved.
“Extra police and specialist units are working on the ground now to build a clearer picture of what took place and work to protect and reassure those in the local community.”
A Section 60 order – which gives police the power to stop and search people in a designated area – has been put in place in Shepherd’s Bush and Notting Hill until later this afternoon.
Police are in the process of informing the teenager’s next of kin and a post-mortem examination will be held in due course.
Anyone with information is asked to contact police on 101, quoting reference 8782/26 June, or call Crimestoppers anonymously on 0800 555 111.
Last night’s death takes the total number of homicides in London this year to 59.
It comes just weeks after the capital was gripped by a killing spree that saw three murdered in 24 hours.
Two teenagers lost their lives in the attacks as they were murdered just 12 minutes apart in gun and knife attacks.