THE parents of a "beautiful young man" killed in an unprovoked attack in King's Cross on the weekend have pleaded with the public to help them find closure.

Holding hands with his new girlfriend, country teenager Thomas Kelly ventured into Sydney's red light district on the weekend and never came home.

The 18-year-old was celebrating a friend's birthday when he was knocked unconscious and left bleeding on the footpath by a passing stranger.

He was rushed to St Vincent's Hospital in a critical condition but on Monday night his parents made the heartbreaking decision to turn off his life support and donate his organs.

Speaking to reporters on Tuesday morning Thomas' mother Kathy said she "wanted everyone to know what a beautiful, beautiful young man he was and how he touched so many lives".

Thomas's father Ralph said his family did not know what day it was and had not changed their clothes since driving to the city from the Southern Highlands on Saturday night.

"It is like being in a hole for us," Mr Kelly said

"We are sitting here today on behalf of our son to appeal to the public to please come forward to help us bring closure."

Thomas was king hit by an unknown man as he was walking south along Victoria St about 10pm Saturday.

Kings Cross Crime Manager Inspector Paul McDonald described the attack as "cruel and senseless".

He said Strike Force Mohawk had been formed to investigate the teen's death.

Anyone with information can phone Crime Stoppers on 1800 333 000.

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