The victim was Louis-Ryan Menezes, from Rothwell, and a Home Office post mortem has indicated that he died from a stab wound to the chest, a spokesman for Northamptonshire Police said on Sunday afternoon.
The incident happened in Drayton Walk in Kingsthorpe.
The three people arrested yesterday in connection with the incident have now been released without charge.
A large-scale investigation is underway, led by the East Midlands Special Operations Unit (EMSOU) major crime team.
The senior investigating officer, Detective Chief Inspector Karl Whiffen, said: “We are in the early stages of this investigation and I have a large team of specialist officers working round the clock to identify and bring to justice whoever is responsible for killing Louis.
“We are keeping an open mind as to the motive and we need the public’s help to enable us to track down whoever is responsible for ending his short life.
“I am appealing for anybody who was in the Drayton Walk area of Kingsthorpe between 6pm and 7pm on Friday, 25 May to let us know if they saw or heard anything out of the ordinary.
“I am also asking for help from anybody who was in or around the Eastern Avenue North or Newnham Road shops area at the times mentioned above, perhaps driving home from work, to consider whether they saw anything untoward or saw people acting suspiciously.
“If you have private CCTV footage or perhaps a dashboard camera, we’d like to hear from you. Your footage may provide important information which could help us piece together what happened around the time of Louis’s attack.
“Our dedicated officers are supporting his family who are naturally devastated about what has happened. We ask that their privacy is respected at this incredibly difficult time.”
Witnesses are asked to call police on 101. Anybody wishing to remain anonymous can call Crimestoppers on 0800 555 111.