Fares Maatou bravely stepped in to protect his friend during a row when he was stabbed in the head outside Zzetta restaurant in Barking Road, Newham.
He was then hit with metal poles before thugs stole his scooter and ran off.
Emergency services were called the scene shortly before 4pm, but despite the efforts of paramedics Fares was pronounced dead shortly after 4.30pm.
The Met Police said they arrested a 14-year-old boy and a 15-year-old boy on suspicion of murder on Friday. Another 15-year-old boy has been arrested in connection with the attack.
The force said officers believe Fares was attacked with “a large bladed item”.
DCI Perry Benton said Fares’ family were “absolutely devastated”.
“I have assured them of my total commitment to bringing to justice those responsible for this senseless killing,” he said.
“They will be supported by specialist officers at every stage of what will be a terrible ordeal for them in the weeks, months and years ahead.
“We have already seen fantastic support and received a good deal of information from local people. I thank them for that, and ask anyone with information or any witnesses who have yet to speak with police to please come forward and tell officers what they know.
“We are piecing together the picture of what happened on Friday afternoon, and every fragment of that picture will be crucial.
“Three boys have been arrested and they remain in police custody. This is a fast-moving investigation and there will be further developments.”
Following the attack, Fares’ friend said he had died while trying to protect him.
“If you knew Fares you would know he was never involved in anything,” he said.
“You died protecting me bro, where I saw you get stabbed and you dropped I looked at you bro thinking they really got him, most f****** part was they even took his scooter.
“Rest in perfect paradise my bro, love you forever.”
Another friend of Fares said he was “kind-hearted and loving.”
"The other boy was going to get hit with a pole and stabbed as well, but Fares jumped in front of him so he wouldn't get hurt,” the 15-year-old pal said.
A restaurant worker described the desperate attempts of bystanders to resuscitate the 14-year-old.
A member of staff at Zzetta restaurant, who did not want to be named, said a FedEx worker, an off-duty police officer and a woman had all rushed to the teenager’s aid as he lay in the street outside the restaurant.
“They were just shouting at him ‘wake up, wake up, try to breath’,” he said, adding that someone started chest compressions while he called 999.
“Three or four of us were all shouting loudly ‘one, two, three’, so there was a rhythm for compression.”
He said the victim, wearing a school uniform, was “totally blacked out”.
“I was hoping he would end up in hospital and stay alive,” the witness added.
Tearful mourners have left flowers at the scene of the fatal stabbing.
A pile of floral tributes and some balloons were placed outside the restaurant, with messages on cards paying tribute to a “brother” and someone who “touched so many”, with one saying: “We miss you a lot we want you back”.
A small group of young people gathered by the makeshift memorial hugging and comforting each other.
A close friend of Fares, accompanied by her mother, joined others paying tribute to him at the scene of the attack.
She said: “He was really nice. He had nothing to do with the gang stuff around here.
“He would just be there for you. If you ever needed him he would be there.”
She added: “He was happy. He loved life.”
Her mother, 33, from Stratford, said her daughter had been left “heartbroken”.
“She hasn’t stopped crying since she found out.”
She said her daughter and the 14-year-old had been friends since nursery and described the boy as a “lovely kid” and a “normal teenager”.
“I’m heartbroken seeing her upset. I can’t imagine what his parents are going through,” the mother added.
According to the Sun, Fares father is also "critically ill" in hospital with Covid-19.
The unnamed friend told the newspaper: "The family have been through so much.
"We didn’t know if his dad was going to pull through after falling terribly ill with Covid.
"He’s still critically ill and under intensive care, and now they have lost their youngest son."
Anyone with information is asked to call the incident room on 020 8345 1570 or to contact Crimestoppers anonymously.