The assault happened between 3am and 3.30am on Thursday January 28 in Union Terrace Gardens.
Last week, police said they were searching for two men seen in the area around the time of the incident and are now appealing for any other witnesses.
Officers said a group of five men and one woman - thought to be students - were seen in Belmont Street at about 3.10am on the night making their way towards the Union Terrace Gardens area.
Detective inspector Jacqui Campbell said: “We are looking to trace these individuals as they may have information that could assist our enquiry.
“They are seen to walk up Belmont Street and towards His Majesty’s Theatre before turning past the Wallace statue towards Union Terrace Gardens.
“Anyone who may have been in the area at the time, or who thinks they have information about the incident, should contact police on 101 or Crimestoppers on 0800 555 111 if you wish to remain anonymous.”