Luke Attard, 17, was attacked on the seafront at Barry Island last week on Monday, May 25.
The incident took place during the busy Whitsun bank holiday when Barry Island was packed with tourists.
Mr Attard had travelled from Cardiff to the popular Welsh seaside resort with friends, but the day ended in tragedy when he was stabbed in the back of his leg.
His cousin, Nicole Attard, said: “Luke travelled to Barry Island with his friends to enjoy the warm weather and spend the day making memories.
“What should have been a normal day for a young man enjoying time with his mates turned into a nightmare.”
The injury was so severe that he was airlifted to hospital and later had to have his leg amputated.
Ms Attard said: “He has since endured multiple surgeries, blood transfusions, and intensive medical treatment.
“Despite the incredible efforts of the doctors and medical staff, the damage caused by the stabbing was so severe that Luke sadly had to undergo a life-changing leg amputation.
“At just 17 years old, Luke has faced more pain, trauma, and uncertainty than any young person should ever have to endure.”
A fundraising campaign has been launched by his family to help support his recovery and long-term needs.
Ms Attard said: “The funds raised will help support Luke with rehabilitation, specialist equipment, mobility aids, prosthetic-related costs, travel to medical appointments, and any additional support he may need as he rebuilds his life, confidence, and independence.
“No amount of money can undo what has happened, but together we can help ease some of the burden and give Luke the best possible chance to move forward and focus on his recovery.”
South Wales Police initially described the injury as not believed to be life-changing, but later confirmed the seriousness of Mr Attard’s condition.
A force spokesman said: “However, he has since had to undergo a life-changing leg amputation and has been subject to critical care at the University Hospital of Wales, Cardiff.”
Detective Inspector Sarah Lee, from South Wales Police, described the impact of the attack.
DI Lee said: “The extent and seriousness of the injury sustained by the teenage victim is absolutely devastating.
“Understandably his family are distraught, and they have been assigned a specially trained family liaison officer for additional support.
“Our investigation, which includes examining hundreds of hours of CCTV footage and tracing witnesses, is continuing.
“An 18-year-old man from Riverside, Cardiff, who was arrested on the day of the incident on suspicion of wounding with intent, remains on bail pending further enquiries.”
DI Lee appealed to the public for assistance in the ongoing investigation.
She said: “We urge witnesses or anyone with information to please contact South Wales Police or Crimestoppers anonymously.”
The family have described Mr Attard as a “kind, caring, and genuine young man” who has shown “incredible courage” during his ordeal.
Police have asked anyone with information about the incident to come forward.
