Officers found Kamal Nuur, 18, suffering from knife wounds at 8pm on Monday in North Road, Islington, on September 14.
He was treated by paramedics but despite their best efforts, Kamal was pronounced dead at the scene.
Scotland Yard said Kamal was chased and attacked in Goodinge Close, just off North Road, by two male suspects who then fled towards York Way.
Detectives have now released CCTV footage showing the pair in North Road at 7.58pm on the night of the attack, and then cycling towards York Way.
The two suspects were cycling at speed and continued into York Way and Brecknock Road, before dashing towards Leighton Road and speeding along the footway.
A post mortem examination confirmed that Kamal died as a result of stab wounds sustained in the attack. There have been no arrests.
A witness described how she tried to save the teenager’s life after he was stabbed following a chase and fight lasting less than a minute.
The woman told the Standard: "I heard a ruckus then a cry of ‘help me help me’. There was a young man laying on the ground. I went out with other neighbours, he was still breathing.
“We tried to comfort him. His friend was with him shouting ‘raise your hand if you can hear me’. He was not conscious. The paramedics arrived very quickly then loads of police.
"There had been a bit of arguing then the boy shouting ‘help me help me’ then footsteps running away, all in the space of 30 seconds.
"I can’t get the image of the boy laying there. The neighbours did their best. It’s heartbreaking, our thoughts are with his family."
Another resident said they heard "a desperate cry" after the victim was chased through the estate, near Caledonian Park, by a group of men.
DCI Andy Partridge, from the Metropolitan Police, said: “These images are significant as we piece together the events that led to the attack on Kamal. He suffered horrific injuries in the attack that took place and was set upon for no apparent reason.
“I believe the public can assist in not only telling us where these suspects were heading to, but also someone will know who they are.
"Such grotesque, brazen acts of violence cannot be acceptable, anyone providing information can have the assurance it will be held in the strictest confidence.
“Those responsible do not deserve any protection; Kamal’s family are shocked at his death and will never come to terms with losing him in such a violent way.”
Any witnesses or those with information are asked to call the force incident room on 0208 358 033 or 101 referencing CAD 7154 of September 14, upload images to the police website, or call Crimestoppers anonymously.