The victim, a 20-year-old woman, was touched inappropriately and propositioned by a man in Blue Fly on New Street, sometime between 11pm and 11.30pm on 9 March 2014.
Officers have released an image of a man who they would like to speak to in connection with the investigation and are urging anyone who recognises him to come forward.
The man is white and was wearing a multi-coloured shirt. It is believed that he is a university student.
Anyone who can help officers with their enquiries is urged to contact North Yorkshire Police on 101 – select option 2 – and ask for PC Rebecca Lund or York police.
Alternatively, information can be emailed to email@example.com
If you prefer not to give your name, Crimestoppers can be contacted anonymously on 0800 555 111.
Please quote reference number 1214003820 when passing information about this incident.