Police have revealed new details on the movements of a missing FIFO worker who failed to board a flight in Perth and instead took a cab to the beach.

William Carter smiled in a photo with his mum before she dropped the 25-year-old off outside Perth Airport T3 about 12.40pm (GMT) on Saturday so he could travel to the Pilbara for his working stint.

But he never made the flight and has not been heard from since.

Bill O'Byrne travelled from Kelmscott to Perth Airport on December 6 but was missing by 2pm that same day after he did not make his flight to Karratha. William Carter posed with his mum being being dropped off at Perth Airport. (Facebook)

Today, police shared that Carter was at the airport for an hour and a half before he left in a taxi about 2.10pm and travelled to Trigg Beach.

He arrived about 30 minutes later and was last seen near a surf club on West Coast Drive, which stretches from South Trigg to Sorrento.

He was carrying a small backpack and wearing a black t-shirt, shorts and black and white sneakers at the time.

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His family and police have serious concerns about his welfare, and anyone with information on his whereabouts is urged to immediately contact 131 444.

Carter is described as being about 174cm tall with a slim build, brown hair and blue eyes.