Police have confirmed to 9News that they believe the driver or an owner of a 4WD which was spotted in the area could have been the last person to see the pair, aged 73 and 74, alive.
Authorities believe that person may have also been travelling with an associate at the time.
A white dual-cab ute seen in the area at the time remains unaccounted for.
Police are seeking more information from anyone who may have spotted the vehicle in the area around March 19 and 20 last year.
The discovery of the drone comes after police revealed days earlier they were searching for an unknown white dual-cab ute, which was parked near the campsite.
Mr Hill left his Drouin home on March 19 and picked up Ms Clay from her home in Pakenham in his white Toyota LandCruiser.
Ms Clay told friends she was going away and was expected to return home on March 28 or 29.
But instead, their campsite was found burnt out, with their mobile phones gone.
Investigators believe the pair may have met with foul play.