Rhys Davies had been walking back towards Cardiff's main bus station
The family of a 17-year-old student say they are "totally shocked" by his murder in a city centre.
Rhys Davies had been out shopping with a friend when he suffered serious head injuries in an altercation in St Mary Street, Cardiff at 1840 GMT on Friday.
Rhys was on a building course at Coleg Gwent in Ebbw Vale and was described as "fun-loving" by his family in Tredegar.
He died in hospital on Saturday. Police want to trace three men and a woman and they are to examine CCTV footage.
A post-mortem examination has revealed that Rhys died of head injuries.
Police said Rhys was walking back towards the bus station when he became involved in an argument with passers-by in St Mary Street, near its junction with Wharton Street.
His family said they were "totally shocked and devastated" by the tragedy.
"We cannot believe that this has happened. Rhys was a fun-loving boy who loved a joke. His family were very important to him and he was a doting and loving son. He loved his brothers and sisters and was a devoted uncle."
The incident happened early on Friday evening
Rhys supported Cardiff City and Manchester United and also watched rugby, wrestling and was a keen fly-fisherman.
"He had many friends who too are devastated by what has happened," said his family, who said they had been "left in a state of shock" and were still trying to come to terms with his loss.
After the attack, Rhys was taken to the University Hospital of Wales but died the following day.
Det Ch Insp Paul Hurley, of the force's major crime department, said the argument took place near to the Ladbrokes shop.
"The reasons for this argument at this stage is unclear however, we know that it resulted in Rhys being assaulted causing him to receive serious head injuries," he said.
Officers are looking to trace three men and a woman in connection with the incident:
The first man is described as white, 23-24 years old, of average build, 5ft 8in to 5ft 9in tall, with dark brown hair, a dark brown goatee beard, wearing glasses, wearing a light coloured jacket and jeans.
He was with a woman aged around 20 with dyed blonde hair and who was possibly pregnant. 5ft to 5ft 5in tall, with dyed blonde hair. She was wearing a dark green hooded top.
The second man is described as approximately 19-21 years of age, of black or mixed race appearance, slim build, 5ft 8in to 5ft 10in tall, wearing a white peaked cap, white hooded top and jeans.
The third man is described as of black or mixed race appearance, 18-20 years of age, slim build, 5ft 7in to 5ft 9in tall, wearing a light coloured peaked hat, light coloured hoody, jeans and trainers.
Det Chief Insp Hurley added: "I would appeal for these people to contact us immediately and also anyone else who was in the vicinity at the time of the incident including a number of people who attended to the victim.
"We are also keen to trace a man who was riding a bike near the incident who appeared to be a workman. He was wearing a black donkey-style jacket and an orange tabard."
Officers are to examine CCTV footage as a main line of inquiry.
Three men originally arrested in connection with the incident have been released on police bail.
Anyone with information is asked to contact the incident room at Fairwater CID on 02920 571530 or Crime Stoppers on 0800 555111.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.