CCTV cameras captured the woman dressed in green body paint as she left the restaurant on Blake Street with a group of other people on April 26.
Police say an assault took place, leaving a 17-year-old local girl with bruising to her face and a black eye.
A spokesman said: “At the time of the incident the woman suspected of the assault was covered in green body paint with dyed red hair. However, she is believed to be a white woman, in her late teens or early twenties and around 5ft 8in tall with a medium build.
Det Constable Cheryl Hunter, of York CID, said: “This appears to have been a wholly unprovoked assault. Thankfully the injuries were not too severe. However, the outcome could have been far more serious.”
Anyone with information should call 101 or Crimestoppers anonymously on 0800 555 111 quoting reference number 12130066826.