The Metropolitan Police said 18-year-old Wali died in hospital on Tuesday after a fatal attack on a playground in Cranford Way, Tokenheim, west London.
Officers are examining CCTV and the force said eyewitnesses testified that he saw a fight on the field moments before he was stabbed.
“We are still working to establish the motives behind this tragic attack and are following in the footsteps of many leaders,” said Vicky Tynstall, chief detective at Specialist Crime Command.
Officers recovered CCTV footage from the area and spoke to several witnesses who described witnessing the fighting in the moments before the attack.
“We know there were a lot of people in the field at the time and I would urge anyone who has not yet spoken to the police to contact us immediately.”
Mr Willie was attacked at around 4.45pm on Tuesday and died at the hospital about an hour later.
Matt said his family has been notified and specially trained officers are assisting him. No arrests have been made.
A relative of the young man from Steinmore said. Evening standard. He came to the UK alone two years ago as a refugee and left his family behind in Afghanistan.
His friend Sahil Kocha added: “He was a very good man. He was very caring and loving. He did not hate anyone.
“He stood up for everyone. I wish I knew why someone was hurting him. He was not a fighting boy.
The attack came after a clash between the victim and the suspects, a few yards from Thomas College in Richmond, who confirmed on Wednesday that the victim was a student.
College Principal Dr. Jason Jones said: “Our thoughts and prayers are with the student’s family and friends at this difficult time.
“This loss will raise many emotions, concerns and questions for our students, parents, staff and the local community.”
Tonkham MP Munira Wilson offered her “deep condolences” to Mr Willie’s family, adding: “Police are pursuing a key suspect who is still at large and the location of the crime. The forensic search continues.
“Access to the field and railway bridge is blocked by Tokenham Rough and will be sealed for at least the next 48 hours.
Police have significantly increased patrols in the area and will continue to do so for the next few days. I urge them to continue to do so after this week. The college’s security team is also patrolling the area.
I will repeat my calls to the Mayor of London and the Home Office to increase local police numbers.
Additional reporting by PA Media