The break-in happened on Sunday, November 6, when a group of six men were walking past the Barcelona Club in Grant Street, at around 6.10am.
Two men then kicked open the door, and five people went inside and stole alcahol from behind the bar after searching the premises.
But bizarrely, an apology note and money were sent to the manager of the club later that day.
The group fled in the directionof the Swashbuckle pub.
A Humberside Police spokesperson said: "All six were said to be between 17 and 23-years-old, white and of slim build. Four had dark brown hair, one was fair haired and the sixth had light brown hair.
"Officers are keen to speak to anyone who can identify the men in the CCTV or witnesses who have yet to come forward."
Anyone with information is asked to call police on 101, quoting crime reference number 2226917.