Some camping gear, including a pack and a sleeping bag, were missing from their Uruti home, she said, but it wasn't clear that her son had taken it.
The police said Karl Roberts appeared to have lost control of his car, a green Subaru Impreza, early on Tuesday afternoon. The car slid down a bank and stopped close to the stream that runs alongside Uruti Rd.
The car was found at 3.30pm, which is thought to have been around two hours after the crash.
Extensive searches were done by Taranaki LandSAR volunteers, a Taranaki rescue helicopter, the police, and family and friends of Roberts.
On Thursday, the official search was suspended and today, the police said: "There is no update."
However, private searches, organised by his family were on-going, Debra Roberts said.
Karl was experienced in the outdoors, she said, but he usually told his parents where he was going and when he would be back.
He wasn't in any trouble and emotionally he was well. He was buoyant and happy - he had applied for a job and had a nice girlfriend. He was working part-time in Urenui.
The crash happened after Karl drove off to check for messages on his cellphone, she said - there is no cellphone reception at the family home.
His cellphone was found in the car - flung into an awkward spot - and his shoes were found on the far bank of the stream.
Karl Roberts is described as a thin Caucasian and around 175cm tall.
Anyone who may have seen him is asked to call the police on 06 759 5500