The boy stabbed to death by a gang wielding knives and swords in Pimlico, central London, has been named as Hani Abou El-Kheir.
Officers were called to the scene at Lupus Street, where the 16-year-old was stabbed, on 6.50pm on 27 January. He was taken to a south London hospital but later died of his injuries.
Witnesses described how the teenager had pleaded for his life before being repeatedly stabbed by the 15-strong gang of teenagers.
Family friend Mahmoud Abosiad said: "He was a lovely boy. He did not deserve to end up on a slab."
A spokesman for the Metropolitan Police said: "A murder inquiry is now under way and an incident room will open in due course, under detectives from the Specialist Crime and Operations Directorate.
"We must retain an open mind re the circumstances of the incident and any motive at this early stage."
No arrests have yet been made in connection with the incident.
Witnesses described how the 16-year-old was running from the gang before he tripped and fell to the floor before the gang attacked him "like a pack of dogs".
Mohammed Alzubaidi, 49, from nearby Peabody Close, said his friend witnessed the attack.
"He said they were carrying knives, some of them with wide swords. He said the victim was screaming and trying to get away," said Alzubaidi.
A second witnesses told the Evening Standard: "We were walking along and saw him running really fast but then he tripped. There were about 15 of them, most wearing dark hoodies and bandanas over their faces. A lot of them were wearing tracksuits.
"They had wide kitchen knives and other knives and they jumped on him like a pack of dogs. He was shouting 'don't do it' but they just went ahead. One put a blade in near his ribs. Others then kicked him before just jogging off as if nothing had happened.
"They put their weapons in socks and then shoved them up their sleeves as they were going. Afterwards they looked calm, one looked straight at me as he was leaving which was scary - we thought they may go for us. We tried to help him as he was lying on the ground."
Councillor Nickie Aiken, from Westminster City Council, said: "Once more we have seen the tragic blight that knife culture has inflicted on the capital.
"Our thoughts are with the family of this teenager and we will offer whatever help we can."
Any witnesses or anyone with any information should contact the incident room on 020 8345 3715. If you wish to remain anonymous call Crimestoppers on 0800 555 111.