A teenager found dead in a shallow grave had studied with one of the woman accused of killing him, Perth police say.

Two women were today charged with murder, a day after police discovered the body of missing teenager Aaron Pajich at a property on Broughton Way, Orelia, in Perth's south.

He was last seen alive at the Rockingham City Shopping Centre, south of Perth, a week ago.

Detective Senior Sergeant Dave Gorton from the Major Crime squad said a search of the Broughton Way property revealed a newly laid concrete pad.

"The concrete was removed and the body of Aaron was found in a shallow grave," he said.

"Two females, aged 42 and 25, who reside at the address have both been charged with Aaron's murder and will appear in the Perth Magistrates Court tomorrow morning.

"Aaron and at least one of the accused studied at the same educational facility in Kwinana."

Police are still seeking a motive for the killing.