A boy has been charged with murder over the death of Jamil Palmer.
Palmer, 18, of Hampton, Middlesex, was stabbed to death after walking through Crane Park in Feltham, Hounslow, on 7 May. He was found in the road near Evans Grove.
The accused, who is 15 and cannot be named for legal reasons, has been remanded in custody and will appear at Uxbridge Magistrates' Court.
A 15-year-old girl and a 16-year-old boy, arrested on suspicion of murder, remain in custody.
An 18-year-old man and a 16-year-old boy previously arrested on suspicion of murder have been bailed until June pending further enquires.
Det Ch Insp Noel McHugh, who is leading the investigation, renewed his appeal for witnesses.
"It is clear that there is a misguided loyalty where some people are not speaking to the police, protecting those involved," he said.
"I would ask those who are reluctant to come forward to do so, so Jamil and his family can get the justice they deserve.
"I would also like to reiterate my reassurance to anyone who has witnessed this horrific attack that my officers are here to protect you and will treat any information you have with the utmost sensitivity and discretion."