Gang members believed to be present when Solomone Taufeulungaki was killed have been asked to look inward at their own consciences and come forward.
Victoria Police on Sunday asked gang members involved in the Deer Park killing to help them identify the person who stabbed the teenager and bring his family justice.
The 15-year-old died on Tuesday after he and his cousin were allegedly approached by a group of about 10 youths armed with knives near Brimbank Shopping Centre.
Seven boys, aged between 13 and 16, have been charged with violent disorder and affray but no one has yet been charged with Solomone's death.
Police said they believed the fatal affray was a result of tensions between two youth gangs in the western suburbs.
It is believed the attack on the teenager is linked to an assault that occurred at the Brimbank Shopping Centre the day before Solomone was killed.
"We know many of those involved simply had miscarried feelings and they were just defending their mates with no intention to kill anyone," Detective Inspector Tim Day told reporters.
"However, at least two people took knives to that incident on Tuesday."
Det Insp Day said anyone who was there and withholding information should feel in some way accountable.
"Unless Solomone's killer is brought to justice, Solomone's blood is on the hands of all that attended at that incident on Tuesday," he said.
Detectives believe some people have mobile phone footage of the fatal attack and are appealing for them to contact police.