The teenager was killed in Chingford at about 9.20pm on Easter Monday, the Metropolitan Police said.
Members of the public and emergency services tried to give first aid but the teenager died at the scene.
A 14-year-old boy has been arrested and two other teenage boys had previously been arrested in connection with the stabbing.
Officers were on the scene within three minutes, along with paramedics from the London Ambulance Service and London’s Air Ambulance.
His family have been told.
The police said they are still awaiting formal identification.
A friend told news website MyLondon a man had jumped out of a car and chased the victim before stabbing him.
He said: “I was with him yesterday and it happened three hours later after I left. We were just chilling, minding our own business.
“I went out with my dad and got home, then got a call saying your friend had got stabbed at the bottom of your road. I could not get past the tape.
“He was with his friend, they were walking this way and a guy jumped out a car and appeared out of the dark, pulled a knife out and started running after them.
“One ran that way and my friend ran that way and the guy targeted him for some reason.”
