Investigations continue but police say it's unlikely Russell Hill and Carol Clay are still alive.

Mr Hill, 74, left his Drouin home on March 19, 2020 and picked up Ms Clay, 73, from her home in Pakenham in his white Toyota Landcruiser.

Mr Hill was last heard from the next day on March 20 via HF radio, stating he was at Wonnangatta Valley in Victoria's high country.

Detectives want anyone who was in the area at the time to contact them, including those at Howitt Plains and Zeka Spur Track on March 19 or 20, or the Wonnangatta Valley and Wonnangatta Station between March 20-24.

Campers found Mr Hill's vehicle with signs of minor fire damage at their campsite near Dry River Creek Track in the Wonnangatta Valley on March 21. The campsite had been completely destroyed by fire.

Police would like to speak to anyone who saw this fire or the smoke from it.

Investigators have been told Mr Hill took a drone with him on the trip, which is yet to be recovered, and they are yet to account for a white dual cab ute seen near the pair's campsite on March 19.

It is still to be determined whether the pair's disappearance is suspicious.

"Sadly, at this stage we believe it is highly unlikely that either Russell or Carol are still alive," Det Insp Stamper said on Friday.

Australian Associated Press