David Williamson, aged 35, was attacked on the playing fields behind Burton Green Primary School in Clifton late at night on Monday 28 May 2012.
Officers believe he was subjected to a prolonged attack which left him in a coma in York District Hospital suffering from severe head injuries.
He was left lying alone on the playing fields until he was discovered by the police in the early hours of the following day.
Since the attack, David has undergone extensive surgery to insert 16 plates into his face to repair the damage he sustained.
He remains seriously ill in hospital.
Four local men, aged 19, 21, 25 and 36, have been arrested in connection with the incident and released on bail. However detectives still need witnesses to come forward to help with their enquiries.
Detective Constable Alan Williams, of York CID, said:
It is clear from our investigations to date that there was a large disturbance in Clifton on the night David was assaulted around the Kingsway North and Burton Green area and I know that people will have witnessed what may have been the lead up to this assault.
A number of people have already provided some vital information about the attack and I thank them for that, but I am sure that there are other people who, for their own reasons, have yet to come forward.
I need those people to do the right thing and speak to me about what happened that night.
Those in the local community know what happened to David, who is responsible and how this attack took place. I am appealing to their conscience. Look at the results of that attack.
I have spent time with David in hospital and have witnessed first hand the effects of what happened to him.
Those responsible must face the consequences of their actions that night.
Anyone who can help officers with their enquiries is urged to contact North Yorkshire Police on 101 – select option 2 – and ask for Alan Williams or York CID.
Alternatively, Crimestoppers can be contacted anonymously on 0800 555 111.
Please quote reference number 12120085883 when passing information about this incident.