A worried mum has shared a selfie taken with her son shortly before he failed to board his flight and mysteriously vanished without a trace.

FIFO worker Bill Carter, 25, caught up with his mother, Jenny O’Byrne, for brunch on Saturday before she dropped him off at Perth Airport Terminal 3 at 12.40pm.

He has not been seen or heard from since.

Mr Carter never checked in for his booked 2.15pm flight to Karratha in northern WA for his latest 12-days-on, 9-days-off stint at the Fenner Dunlop mine.

Family, friends, and colleagues have serious concerns for his welfare, as he had been enduring struggles with his mental health.

Originally from Bunbury in Western Australia‘s far south-west, Mr Carter had just returned from a well-earned holiday in Zambia to visit his father.

He posed for a selfie with his mum so she could share it with his sister just 20 minutes before she dropped him off at the airport.

Ms O’Byrne said Bill had been struggling with his mental health and had recently come off anti-anxiety medication.

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Bill Carter posed for this selfie with his mum Jenny O’Byrne just 20 minutes before he vanished from an airport without a trace

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Bill and his sister had just returned from visiting their father in Zambia

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Bill was a FIFO worker at the Fenner Dunlop mine in Western Australia’s Pilbara region

She added that her son appeared to be ‘still quite sad’ while holidaying in Zambia.

‘He’s not well, and he’s very vulnerable and at risk and we just need a lot of people to keep their eyes out,’ she told Perth Now.

‘But there’s been some other things that have gone on in his life, a situational crisis.

‘He’s been going through some challenges recently and because he’s so quiet in nature, some of those challenges have been missed because he’s not very talkative.’

Ms O’Byrne believes her son may have called or messaged someone at 1.05pm before his phone was switched off 40 minutes later.

She urged everyone to reach out to loved ones in the lead-up to the festive season which can be lonely or difficult for some.

Mr Carter is white, 174cm tall, slim build, with brown hair and blue eyes.

He only had a small 5L bag with him as most of his belongings were at the mine site.

Anyone with any information about Mr Carter’s whereabouts is urged to contact police on 131 444.

If you or someone who know needs support, call Lifeline on 13 11 14 or SANE Australia on 1800 187 263.