Police now have aerial photographs of remote Coober Pedy in the South Australian outback, which have prompted them to plan another search for the body of a teenager who was last seen alive in 1990.

A 42-year-old man, arrested late last year at Mount Gambier in SA, faces a charge of murdering 16-year-old Karen Williams, but her body has not been found.

Detective Superintendent Des Bray from the Major Crime Investigation Branch said two witnesses had come forward with new information since a previous outback search was made.

Last year detectives used a ground-penetrating radar to check an area and then dug in several locations, but nothing significant was found.

Detective Superintendent Bray said local outback police and council workers, along with Major Crime detectives and a State Emergency Service mines and rescue team, would dig up two more areas in coming days to check several old mine shafts.

He said the aerial photos now given to police were taken about the time the teenager disappeared and had helped them redefine the search zone.

"We still believe the most likely place to find Karen is within a 150-metre radius of the junction of Maliotis [Boulevard] and Flat Hill Road at Coober Pedy, just on the outskirts of Coober Pedy," he said.

"Importantly, information that we now have is that from the burial site on the night the offenders could see the Opal Inn Hotel in a direct line of sight."

Karen Williams was last seen alive in 1990. ( SA Police )

Detective Superintendent Bray said the latest search would start on Monday.

"We will be using a big grader to remove the topsoil to identify closed-in [mine] shafts," he said.

"How long it will take will depend on how many shafts we find that we have to excavate, but typically it would take a day to do a couple of shafts if we don't experience any difficulties."

Karen was last seen alive between 5:00-6:00am on Saturday August 4 in 1990 and her disappearance was declared a major crime in October 1990.

A $200,000 reward has been offered to anyone who can lead police to the discovery of her remains.