Police have pleaded with drivers who may have seen missing German tourist Monika Billen to come forward, saying they should not assume that other people were going to step up instead.

Key points: Police are concentrating the search on the Emily Gap area, about 15km east of Alice Springs

Police are concentrating the search on the Emily Gap area, about 15km east of Alice Springs Monika Billen has been missing since New Year's Day and police want information about her last movements

Monika Billen has been missing since New Year's Day and police want information about her last movements Anyone with information should call 131 444

The last confirmed sighting of Monika Billen, 62, was by staff at the Desert Palms Resort in Alice Springs, where she had been staying for more than a week.

But after failing to check out and missing a scheduled flight to Darwin on January 5, her disappearance was reported to police on January 8.

On Friday, police said they have footage of eight cars driving past Ms Billen as she walked down Barrett Drive on New Year's Day, but said none of those drivers have contacted them.

"We are very concerned we are getting very little information come in from the Alice Springs people in relation to whether they've seen Monika or not," Acting Superintendent Pauline Vicary said.

"Just don't assume that other people are going to tell us and you don't need to.

"Particularly there are eight vehicles that drove past her on Barrett Drive on the first, none of those people have contacted us.

"We are urging you please contact us so we can have a conversation, you may have seen something and not even realised it."

Police received reports of two sightings of the missing tourist on Thursday — one said they gave her a lift to Olive Pink Botanic Gardens on January 2 and another said they spotted her at Emily Gap on January 1.

Map Police are searching the Emily Gap area for missing tourist Monika Billen

Superintendent Vicary said they on Friday focussed search efforts around Emily Gap, a popular tourist site about 15 kilometres east of Alice Springs, after doubts arose about the timing of the Olive Pink sighting.

"So at the moment we're focussing on Emily Gap as the first scenario, so we have helicopters, motorcycles and drones out here today to try and find any evidence that she is out this way," she said.

"We are trying to clarify some information in relation to the timing that Monika was dropped off at Olive Pink.

"And that may have actually been earlier than anticipated now."

She said they may revisit that lead once the timing issues had been clarified.

Police were also working with cattle station workers and Aboriginal communities along the Ross Highway and will be door-knocking residents, asking for information.

Superintendent Vicary said they have now been in touch with Ms Billen's brother in Germany, but said the family's plans are not clear at this stage.

She said they are not yet treating the disappearance as suspicious.

Police have focused the search for Monika Billen to Emily Gap, east of Alice Springs. ( ABC News: Katrina Beavan )

Red top, cashmere scarf

During a search of her room, police found brochures for walking trails, including the Larapinta Trail, leading them to believe she may have gone hiking.

Ms Billen is described as being of Caucasian appearance, slim build, with short grey hair, and was last seen wearing a red chequered long-sleeve top, denim knee-length shorts and a bright red backpack.

She was also wearing a yellow cashmere scarf over her head and shoulders to protect her from the sun and heat.

Police urged anyone who may have seen Ms Billen or who have any information as to her whereabouts to contact them on 131 444.