It occurred at approximately 7pm on Sunday 21st August 2011, in the beer garden of the Nag’s Head public house on Micklegate.
Three men arrested in connection with the incident, have now been released on police bail to allow for further enquiries.
PC Dave Scaife, of the York Safer Neighbourhood Team, said:
I am urging the victims of this assault to come forward and contact the police as a matter of urgency. I also ask that anyone who may be able to identify them to get in touch as soon as possible.
I am still keen to speak with anyone who witnessed the assault and has not yet come forward.
If you can assist with this investigation please contact PC Dave Scaife of York police on 0845 60 60 24 7 quoting reference number 12110141762. Or call Crimestoppers anonymously on 0800 555 111.
CCTV still of one of the victims