Hospital security guard Aidan Becker, 22, was fatally stabbed at Mernda train station in Melbourne's northeast on Friday evening after rushing to the 14-year-old's aid.
The off-duty security guard escorted the boy away from the group but was allegedly pursued and attacked on his way out from the station.
Despite the efforts of paramedics, Mr Becker died at the scene.
Dozens of bouquets and several handwritten notes have been left near the site of his death, with local residents hailing him a hero.
'I've been living here for a few years now and I've never seen anything like it," local father Ameya, who did not want to share his last name, told AAP after laying flowers at the site on Monday afternoon.
"It shouldn't take a hero to keep people safe."
The incident revived painful memories for Lalor mother Jane Lazz, whose own son died at the age of 23.
"It was under different circumstances, but I know the pain of it and the consequences for a family," she told AAP.
"It changes your life to lose a child," she said, adding her son had played for the same football club as Mr Becker.
She became visibly emotional after taping a note to the wall above the makeshift shrine.
"I wrote to thank him for his kindness and courage in helping another person of only 14 and to say they didn't deserve to die in such a way," she said.
"And a few words to the family to say take care of yourselves with the grief to come, because I know what that's like."
Four male teens were arrested at the scene on Friday evening and have since been charged with murder and armed robbery.
The eldest, Mike Pikos, 18, appeared before Melbourne Magistrates Court on Sunday and was remanded in custody to return to court on June 24.
A 16-year-old from Whittlesea, a 17-year-old from Geelong and a 17-year-old from the City of Yarra have also been charged with murder and armed robbery.
They will appear at a children's court at a later date.
The incident has sent shock waves through the Mernda community.
Local mother Dana said she does not allow her kids to walk around the Mernda area unattended and the alleged attack had added to her fears.
"I don't feel safe here," she told AAP.
"It's just heartbreaking and we all know something needs to change."
On Sunday, Victorian Premier Jacinta Allan announced a Violence Reduction Unit would be deployed to Mernda.
Based on similar models in the United Kingdom, the unit is designed to identify and address the root causes of violent youth offending.
It began operations in Mernda on Monday, where it would work with police, schools and the community to understand the factors behind the incident and to prevent further escalation, Ms Allan said.
Opposition Leader Jess Wilson said the incident was the result of the Allan government's failure to address Victoria's "crime crisis".
She cited an alleged machete attack in Melbourne's CBD in the early hours of Monday, three days after the Mernda incident.
Emergency services rushed to the Queen Street area following reports of a man armed with a machete about 2.40am.
It is alleged an armed 25-year-old Manor Lakes man assaulted another man, who was taken to hospital with minor injuries.
The 25-year-old was charged with affray and intentionally causing injury and remanded to appear at Melbourne Magistrates Court on Monday.
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