The family of a young man found unconscious in a Karratha car park earlier this month has pleaded for witnesses to contact police.

Detectives are investigating how Ben Gabriel, 29, ended up seriously injured metres away from the Karratha nightclub he had attended with friends.

A member of the public found Mr Gabriel unconscious in a car park off Warambie Road in Karratha on the morning of Saturday, 2 March.

He was later flown by the RFDS to Royal Perth Hospital where he remains in a coma in a critical but stable condition.

Mr Gabriel's step-father, Tony, says the family is desperate to find out what happened.

"Ben's only a 20 year old boy, or a young man," he said.

"He's got a long life in front of him. It's never going to be the same again. Never.

"Not for Ben, not for his family, not for his friends."

Detective Adrian Richards says Mr Gabriel suffered injuries to his face and upper body.

"I won't go into any further description in regards to that but yes he's not in a good way," he said.

The local State Emergency Service spent two hours last night combing the area in Warambie Road for clues that could help police piece together what happened.

Detective Richards says they completed a thorough search.

"They will sift every rock. They do it all the time. We use them regularly as a resource," he said.

Detectives say they seized a few items in the ground search and are undertaking tests to find out if they are related to the incident.

Friends held a fundraiser for Mr Gabriel's family on the weekend.

Police would like to hear from anyone who may be able to provide further information about Mr Gabriel's movements before he was attacked or from anyone who was in the vicinity of the Evolution Lounge Bar on Warambie Road the morning he was found.