Teenager stabbed to death in front of party-goers in North West London
The 17-year-old died at the scene in Brent
Detective Chief Inspector Mark Rogers, of the Metropolitan Police said: "We believe that there was a fight following a birthday party, which would have been attended by a number of people.
"I would urge anyone who was there, and who has not yet spoken with officers, to please come forward. It is vital that we establish what happened.
"I would also ask that anyone who may have captured any of last night's events on their phone to also contact officers."
The teenager's family has been informed but no arrests have yet been made.
Chief Superintendent Dan Knowles said: "I know that the community will be shocked by this incident in which a young man has lost his life.
"We shall be working with our colleagues from Specialist Crime to ensure that this investigation proceeds as quickly and thoroughly as possible.
"Local residents can expect to see an increased police presence in the area and I would encourage anyone with information, or concerns, to speak with them."