Police have found no sign of missing Palmerston North man Brett Hall and are not ruling out foul play as the cause of his disappearance.

The 47-year-old man was last seen on May 29 at his lifestyle block off River Road, north of Parakino, 20km from Wanganui, and was reported missing two days later.

Searchers began their sixth day of looking for him today and police now say there could be "sinister explanations" behind his disappearance.

Senior Sergeant Darcy Forrester said it was still a search and rescue operation to find a missing person.

"However, as time goes by we would be naive not to consider other, perhaps more sinister explanations for his disappearance," he said.

About 20 police and volunteer Land Search and Rescue personnel have been scouring a 16sq km area including rough terrain for any signs of Mr Hall.

They have been joined for the past couple of days by six army personnel with search and rescue expertise.

Police yesterday released a photo of Mr Hall and appealed for public health in tracing his movements.

They particularly want to hear from anyone who had seen Mr Hall or his 2004 Toyota Hiluxs red double cab vehicle with a white canopy, in the past week or two.

The Toyota and a quad bike remain at the lifestyle block leading police to believe he had not left the area.

Mr Hall is described as Caucasian, 1.82m tall and of medium build.