Police have concentrated their search efforts in the Lower Molonglo Nature Reserve, after tracking the 19-year-old's mobile phone.

Detective Sergeant John Giles said text messages Ms Bautista sent to family and friends before she disappeared are of "extreme concern".

He said they have "spared no resource on this investigation", using helicopters and cameras to narrow down the search area.

The Gordon resident was last seen in Chapman at about 8am after spending the night out clubbing in Civic with friends.

"She arrived home to the Chapman address at around 7am, at around 7.30am she had a conversation with her boyfriend and shortly after she left that address and sent some texts to her boyfriend and to her family members," Detective Sergeant Giles said.

"Her mobile phone as last activated about 11.33am on Saturday morning, the best we can tell about that activation was that it was at a location west of the Telstra tower. How far west it was we don't know, our search efforts today have been concentrated on bushlands."

Police are concerned Ms Bautista has attempted to harm herself or has run away.

Detective Sergeant Giles said there is no information at this stage to suggest she met with foul play.

Ms Bautista was last seen wearing a white crop top, black jeans, an oversized denim jacket and a flannelette shirt.

She was driving a black Hyundai i30 bearing the registration number YHE47L.

Detective Sergeant Giles has asked the community to be vigilant and report any possible sightings of Ms Bautista.

"I think people may have inadvertently seen her and passed her almost by accident," he said.

"We're asking people in the wider community, particularly west of Canberra, to be mindful of Kathleen, to be mindful of the black 2010 Hyundai i30 that she's driving to be vigilant in those areas and just keep an eye out for her."

Anyone who may have seen Ms Bautista is urged to call police on 131 444.

When providing information, please quote reference number 5852227.