Police said they were seen at their home in Whakamaru by family and friends at 8pm on Sunday night.
Their vehicle appeared to have been heading towards Whakamaru, suggesting that they had left the settlement to an unknown destination and were returning.
Their vehicle was discovered only today by contractors working at a forest area on State Highway 32 near Whakamaru this afternoon.
It appeared to have left the road and hit a tree. It had travelled some metres from the road and could not be seen from the road.
Police said it was not clear at this stage when the crash happened and police wanted to hear from anyone who knew of the family's movements between Sunday night and today.
Police also wanted information from anyone who saw their vehicle, a green Honda Integra, in or around the area since Sunday.
Taupo Area Commander Inspector Steve Bullock said: "This is an absolute tragedy; a Christmas in ruins for a number of families and friends. Our hearts go out to them.
The crash scene was about 30km from where two people were killed in another smash on State Highway 1 today.
In that crash, at 1.05pm, a car travelling south towards Taupo hit an oncoming truck head-on.
The occupants of the car, two Indian men who were visiting New Zealand, died at the scene.
The male truck driver, and a female passenger, both from Kaitaia, were treated for minor injuries at Tokoroa Hospital.
Assistant Commissioner Road Policing Dave Cliff said the crashes were a devastating prelude to the Christmas Holiday period, which begins officially next week.
"Our thoughts are with the families of those who have died in these terrible and tragic circumstances. This is a devastating loss and a horrific start to the Christmas period, especially as we focus on trying to reduce the rising road toll and make our roads safer," Mr Cliff said.
"While we don't yet know all the circumstances leading up to these crashes, it's a sobering reminder that we all need to do our part in staying safe on the roads.
South Waikato Mayor Neil Sinclair said such a loss of life was a total tragedy so close to Christmas.
" ... to lose what sounds like a family and two other people just before Christmas is shattering. I cannot imagine what it would be like for their families."
Mr Sinclair said people needed to take great care on rural roads, making sure not to rush, to make sure they made it to their destinations safely.