Nicole Liedke has vowed to 'never stop looking' for her missing brother Patrick after the disabled man went missing in bushland on the Queensland-NSW border in April

The sister of a man with complex mental health needs who is missing in bushland on the Queensland-NSW border has vowed she will never stop looking for him, as a massive 13-day community search got underway.

Patrick Liedke, 39, was last seen walking on Piggabeen Road in Piggabeen, west of Tweed Heads on April 23.

Hoping that a renewed focus will finally help find her beloved brother, Nicole Liedke used a Facebook page to call for experienced hikers and trackers to join the search.

She described her brother, who has a disability and is neurodiverse, as a kind and gentle person who loves painting and golfing.

He is Caucasian, 183cm tall, with a solid build, brown eyes, brown thinning hair and a bushy red-brown beard, though his appearance may have changed due to time spent in the bush.

Ms Liedke believed he went into the bush to find some peace. 'I don't believe he chose (to go missing). 

'It pulled him in, in an overwhelming need to be somewhere calm,' she told 9News. 'Nature gives us the perfect amount of everything, it's our natural state.' 

Her brother's car was found on April 26 on a property at nearby Cobaki, with NSW Police, SES and the Volunteer Rescue Association starting a search the next day.

Ms Liedke found fresh barefoot footprints on Tomewin Mountain Road in Currumbin Valley while searching with family across the border in Queensland on April 28, leading to the Queensland authorities joining the search.

But the official searches on both the NSW and Queensland sides were suspended by May 1.

Since then, Ms Liedke has coordinated community searches with help from volunteers, local property owners, infrared cameras and trackers with dingoes.

She said searches by the authorities did not go far enough, given the size of the area and the difficulty of the terrain. 

Ms Liedke also believed the official searches were held back by the 'invisible' border between the states.

'People think the police search until the person is found but that's not how decisions are made,' she said.

Though her brother is at ease in bushland, she said, he could easily have got lost and may have disorganised thinking.

'The people who go missing are vulnerable, especially the neurodiverse,' she said. 'He's not like a lost hiker who is going to sit around and wave for help.'

His phone account activity suggested Mr Liedke may have tried to use Google Maps to get out of the bush.

The last person to see him was a farmer, who saw him covered in mud and looking 'disorientated'.

'He said, "Are you okay?" and my brother didn't respond, he kept walking down Piggabeen Road,' Ms Liedke said. 'He was still so close to his car then.'

The longer he is missing, the wider the potential search area becomes, she said.

'I'm tired. I've been walking every day searching, door-knocking, driving around.

'I'm never going to stop looking for my brother. '

The 13-day community search started on Saturday.

Anyone interested in joining the search can contact Ms Liedke via her Facebook campaign Find Patrick Liedke.

Anyone with information should contact the police in Tweed Heads on (07) 5506 9499 or Crime Stoppers on 1800 333 000.