Police are treating the disappearance of Trish Graf as a major crime. (HANDOUT/SOUTH AUSTRALIA POLICE)Police are treating the disappearance of Trish Graf as a major crime. (HANDOUT/SOUTH AUSTRALIA POLICE) Credit: AAP

The disappearance of a mother of two has been declared a major crime, three weeks after her car was found abandoned at a remote outback location.

South Australian Major Crime detectives have outlined the last known movements of Andamooka woman Trisha Graf, 41, whose Ford Territory was found perched on a dirt mound near a dam on December 12.

Ms Graf had left the Roxby Downs Hotel at 12.19am on December 12 in her car, accompanied by a friend.

While driving towards Andamooka, the vehicle was damaged in a collision with a kangaroo. They continued their journey and visited a home in Andamooka.

Ms Graf left that house just before 2am to travel the short distance to her home and was last seen driving along Dunstan Drive, Andamooka.

Just after midday on December 12, Ms Graf’s partner and a friend found her car abandoned and unable to be driven near Blue Dam, east of the town.

Police are hoping to speak with people who were with Trisha Graf at the Roxby Downs hotel shortly before she disappeared and people who saw her return to Andamooka.Police are hoping to speak with people who were with Trisha Graf at the Roxby Downs hotel shortly before she disappeared and people who saw her return to Andamooka. Credit: Supplied Source Known

Police have conducted an extensive search of the area including the dam, with specialised drones used.

“These searches have failed to locate any remains or any trace of Trisha,” Major Crime Detective Superintendent Darren Fielke said on Tuesday.

“This is highly unusual and particularly out of character for her. Police are now treating the disappearance of Trisha as suspicious, and we hold grave concerns for her welfare.”

Ms Graf lives in Andamooka with her partner and two young children.

Supt Fielke said she was “a very good mother” and her home was in “pristine condition”.

“It is out of character for not to be in contact with her children, and not to be in contact with her partner. Her bank accounts not having been touched,” he said.

Forensic analysis was being conducted on the car.

Police, the SES and community members searched for Trisha Graf after her car was found abandoned at Blue Dam, but have failed to find the missing woman.Police, the SES and community members searched for Trisha Graf after her car was found abandoned at Blue Dam, but have failed to find the missing woman. Credit: Supplied Source Known

“Her thongs were found with her vehicle and we would have expected to locate her if she had simply wandered off a short distance,” Supt Fielke said.

“(Declaring the disappearance a major crime) will allow more specialist resources to be committed to both determine what has happened to Trisha and locate her.’‘

Detectives have spoken to a number of people known to Ms Graf, along with locals from Andamooka and Roxby Downs.

“We are still seeking information from people who were with Trisha at the Roxby Downs Hotel shortly before her disappearance and those who saw her after she returned to Andamooka,’‘ Supt Fielke said.

Anyone with information about Ms Graf’s disappearance is urged to contact police.