UPDATE: WIMMERA police believe two suspects allegedly involved in a car theft, tractor theft and two high-speed pursuits have stolen a third vehicle.
Nhill Senior Constable Les Newton said a light gold Nissan Pulsar was reported missing from a farm north of Nhill about 3.30pm on Monday.
"It was last seen in the Rainbow-Yaapeet area," he said.
The car has yet to be recovered.
Sen Const Newton said two suspects were still at large.
Horsham Highway Patrol Leading Senior Constable Heath Martin said police were looking for a bald Caucasian man, aged about 40, roughly 170 to 180 centimetres tall.
The man has a medium build and an unshaven face.
"We're also looking for an Aboriginal or Torres Strait Islander woman, in her 20s, with dark hair," Leading Sen Const Martin said.
The woman is about 170 centimetres tall and of medium build.
Police found a 2006 John Deere 8330 tractor, which went missing at the weekend, abandoned near Peakes Three Chain Road in Nhill about 3.40pm on Monday.
The two people believed to have stolen it were nowhere to be found.
Police believe they first encountered the pair driving an allegedly stolen red Kia Cerato rental sedan on the Western Highway between Stawell and Horsham about 10pm on Saturday.
Horsham Sergeant Jason Bergen said Stawell police initiated a pursuit after the car failed to pull over.
"It just so happened a Northern Grampians Highway Patrol vehicle was nearby, and that took over,'' he said.
"The pursuit went on for about 12 kilometres, until it was terminated when the car reached speeds of up to 175 kilometres."
Sgt Bergen said Horsham Highway Patrol detected the vehicle about 20 minutes later, travelling at excessive speed on Stawell Road in Horsham.
"They followed it out of town, still heading out on the Western Highway towards Dimboola," he said.
"Yet again, when police attempted to intercept the vehicle, it sped up and took off.
"The pursuit was terminated when the vehicle turned its lights off and drove on the wrong side of the road."
By this stage the car was almost at Pimpinio.
Sgt Bergen said the car would have been travelling about 165 kilometres an hour.
"The vehicle was later seen travelling through Nhill about 10.50pm," he said.
"At this point, I issued a directive that no further pursuits occur."
Horsham Highway Patrol Leading Senior Constable Heath Martin said police found the red Kia sedan abandoned on Lorquon Road at Lorquon at 7.10pm on Sunday.
He said two people were seen in the area between Lorquon and Nhill on Sunday afternoon.
An extensive police search failed to locate the pair.
Leading Sen Const Martin urged anyone who might have seen the pair to call Crime Stoppers on 1800 333 000 or Horsham Police Station on 5382 9200.
"If anyone in the area has any vacant houses or farm properties that there has been any suspicious activities at during that time, they could also report it," he said.