Missing New Zealand nurse, Louisa Akavi, may be too scared to reveal herself to authorities.

The Red Cross has revealed Louisa Akavi was taken hostage in Syria by ISIS in 2013 - and still hasn't been found.

At least two people have described seeing the nurse in December, at a clinic, in one of the final villages held by Islamic State.

It's believed she may now be in a camp in Northern Syria.

Emma Beals is a Journalist specialising in aid work in Syria and told Tim Dower after five and a half years as a hostage she may be afraid to come forward.

"There have been sightings of her throughout her captivity that have been verified to differing degrees. The common understanding is that she is alive, she certainly was believed to be alive in December."

"She has been a hostage for five and a half years, it's a very long period of time to build up fear in a person. We don't know what they may have said to her, she may be very frightened of them," she said.

The camp Louisa is believed to be in is made up of 70,000 people, most of whom are ISIS families. Beals said that may be contributing to her not coming forward.

"She may be very fearful of them, they have treated her very poorly to date. So I don't think we can make any judgements about why she may or may not have made herself known if she is in that camp."

She said it's hard to know whether naming her was the right call.

"There's no right answer in these cases. It's something that those that are close to Louisa, her family, her employer, the Government, need to make in consultation with each other and do what they think is best for her."

Beals said pressure from international media has been mounting, which made it incredibly difficult for the Red Cross to keep her identity a secret.

"That position has been held very firmly for five and a half years, and became increasingly difficult and I think there was a decision taken to use that pressure to try and find some information that might help to bring her home."