A private investigator trying to find missing Marokopa man Tom Phillips says he'll likely hide again, after being spotted.

Phillips disappeared 18 months ago with his children Jayda, Maverick and Ember.

He was seen yesterday in Te Awamutu, Te Rapa and Kawhia in Waikato - driving a stolen bronze Toyota Hilux flat-deck ute.

Police still haven't found him or his children.

Investigator Chris Budge says he says he's afraid Phillips will now do something silly.

"Because he's feeling caged, and I know that that is well and truly at the police's front of mind. That has been at the police's front mind for some time, of the unknown actions that could occur."

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