Family and friends of Paul Miller have set up a Twitter page to ask for more efforts to be made to find him.

Miller went missing after leaving for a hike in Joshua Tree National Park in California on July 13.

An intense search was carried out for five days by land and air, with 90 searchers, helicopters and dogs involved at its peak.

The search was subsequently called off.

The social media page was set up to call for more work to be done, up to and including FBI involvement.

“There is that small possibility that there has been some kind of criminal activity involved in his disappearance,” said family friend Ainsley Otten.

The movement has received an outpouring of support from a group Californians who are doing what they can to help.