Sara Okerstrom was washing the dishes as her partner of 10 years Matthew Williams said goodbye before driving off in his red Toyota Hilux to go gold prospecting in Lerderderg State Forest last Sunday.

He had left her $20 to pick up a packet of cigarettes for him and was expected to return that afternoon.

It was the last time she saw him.

The alarm bell was raised when he failed to return home at 1pm when they had organised to go to the swimming pool.

Ms Okerstrom has been "numb" since.

"I'm in a scattered, tormented state. My whole world is upside down at the moment," Ms Okerstrom said.

"I can't see how I'm going to cope if he doesn't come home.

"I'm clinging to the hope that he is just down a mineshaft. I have had trouble not going to those dark places."

Rather than opening presents on Christmas Day, Mr Williams three-year-old son Ari played in the yard, without knowing why Santa's visit had been postponed.

"He (Ari) is pulling me through, because I know that I need to be strong for him. That's what his dad would want," Ms Okerstrom said.

She said the support from the community and family had been remarkable, with dozens of volunteers and a private helicopter continuing to search on Saturday.

The 37-year-old man left his McLennan Street home in a red Toyota 4Runner Surf twin cab utility, with registration FNK 642 and a distinctive 'Destroyer 666' sticker on the rear window on Sunday, December.

Despite a thorough search of the Blackwood area, his car has still not been found.

He is caucasian in appearance with long brown greying hair, possibly in a pony tail and a short goatee beard.

Mr Williams is of medium build, has a 'pot belly', blue eyes and is 179-centimetres tall.

Moorabool Police Crime Investigation Unit are now leading the investigation into the disappearance of Matthew Williams and are urging anyone with information to contact 5366 4500.

david.jeans@fairfaxmedia.com.au