An 18-year-old man was assaulted by another man inside and outside Maggie's Bar on Commerical Street in Halifax.
It happened on Thursday, December 27 at about 2.10am.
The teenager was taken to hospital for treatment for injuries to his face.
Police have today (Wednesday, May 1) released details of the suspect.
He is described as white, about 25-years-old, with a stocky build and short hair.
He was wearing a white t-shirt at the time of the attack.
Police enquiries are ongoing and CCTV is being examined.
West Yorkshire Police are appealing to anyone who witnessed the incident or has any information to contact them via 101 quoting crime reference number 13180646472.