Police are searching for a 17-year-old boy in relation to the fatal stabbing of teenager Pasawm Lyhym in Sunshine, in Melbourne's west, last week.
Pasawm, 16, was stabbed during an altercation between two groups at Sunshine Place on May 18.
He was treated by paramedics but died at the scene.
Another 16-year-old boy from Sunshine North was taken to hospital with minor injuries.
Police are looking for Hillside teenager Mayik Atem, who has not returned to his home since Friday.
He is described as 185 to 190cm tall with a slim build and black hair in a dreadlock style.
Detective Inspector Dean Thomas said authorities will allege Mr Atem was "a significant player" in last week's stabbing.
He warned anyone found to be harbouring the suspect could face criminal charges and appealed to the teenager to turn himself into police.
"If you are harbouring or assisting Atem to avoid speaking to police, they may find themselves subject to accessory to this murder," he said.
"We don't know if Atem is armed, but we ask if anybody sees him, please do not approach him."
'Tit-for-tat incidents'
Police said the incident involved groups from different schools, and they raised concerns about retaliatory violence.
Police said the motivation behind the incident remains unknown.
"We do believe there were two groups involved in tit-for-tat incidents in the lead up to last Thursday's stabbing," he said.
Inspector Thomas said Mr Atem's family has been working with police to try to locate him and have fears for his safety.
Police share the same concerns that Mr Atem could be the target of retaliation while he remains at large.
"It's certainly a possibility, there's no doubt about that. While he does remain in the community he is a risk and there's a risk to his own safety."
Inspector Thomas said social media activity will form part of the homicide investigation.
"We're talking here [about] a lot of youth offenders. They live with families and I strongly appeal to the families of these people to take some control of their kids," he said.
"What we seem to see is some of these young people, they like to put their escapees on there [online]… so we're certainly aware of that and investigating that."
Detectives have already interviewed a 17-year-old Caroline Springs boy and an 18-year-old from Burnside over the stabbing incident.
Both have been released without charge pending further inquiries.
Schools and Sunshine community on alert
The principal of Caroline Chisholm Catholic College in Braybrook, Rob Brennan, told families of students at the school that there would be a security presence at the campus and regular police patrols in the area.
"A professional security assessment of the college sites has also been carried out today," he said.
"I have also reminded students about our college's behaviour expectations and policies relating to safety.
"The college has today continued to work closely with our nearby schools, and with community leaders, with the aim of supporting the ongoing safety of all in our local community."
Maribyrnong Mayor Sarah Carter said the council was working with police to ensure the safety of students in the area.
"There are real concerns around how the community is feeling and how parents and students attending that school and other schools in the area are going to feel about their safety because it was an absolutely shocking fatality and attack," she told ABC Radio Melbourne.
Police have asked anyone with information about the incident to contact CrimeStoppers on 1800 333 000.
