The 18-year-old suffered a serious injury to his nose and had to be taken to hospital for treatment after being attacked near the Westquay entrance on Above Bar Street.
He was with two friends when a group of around 15 people, unknown to them, approached them at around 8.30pm on Monday.
The man has since left hospital but police are appealing for witnesses to track down his assailants.
A police spokesperson said: “Officers investigating this incident would like to hear from anyone who was on Above Bar Street at around 8.30pm on Monday evening and saw what happened.
“Perhaps you saw the assault itself, or maybe you saw the events leading up to it or the aftermath? Perhaps you saw the large group of people in the area?
“We would also like to hear from anyone who may have CCTV footage from the area who has not yet spoken to officers.”
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The first suspect is described as: aged between 17 and 22 years old; white; 6ft tall; of stocky build; with ginger hair; wearing a dark/black short sleeved t-shirt and dark trousers/jeans.
The second suspect is described as: aged between 16 and 19 years old; 5ft 6ins to 5ft 9ins tall; mixed raced; of slim build; with dark curly hair (relatively long but did not come past his ears); wearing a grey hooded jumper and grey Nike Tech tracksuit top.
The third suspect is described as: aged between 16 and 19 years old; 5ft 10ins tall; white; of average/larger build; with blonde, short hair; wearing a grey hooded tracksuit top and white short sleeved t-shirt.
Police would also like to speak to a female who was seen in the area at the time and may have information to assist their enquiries.
She is described as: aged between 16 and 19 years old; 5ft 5ins to 5ft 7ins tall; mixed raced; of skinny build; with long dark brown/black hair worn down.
Anyone with information is asked to call 101 quoting reference 44230298298.
Alternatively, submit information online at