An Australian yoga teacher whose ex-partner vanished with their three-year-old daughter after flying to Britain has appealed for help from anyone with links to "alternative communities".
Peter Uhd, 57, said he believes Victoria McKay, 43, and Ruby McKay-Uhd are living in a camper van.
He said he is "desperate" and has urged anyone with information about the pair to help.
The girl had been at the centre of family court proceedings involving her mother, also a yoga teacher, and father in Australia.
"Please, anybody who may have been at a camp ground, has links with alternative communities or lives in a farming area who may know their whereabouts," said Mr Uhd, who lives in Melbourne.
"I'm a desperate father who just wants to see my little girl again.
"I am desperately worried about her living in a van."
A UK High Court judge overseeing Ruby's case had earlier this week raised the alarm.
Mr Justice Keehan, who is based in the Family Division of the High Court in London, said on Tuesday that he is very concerned about Ruby's welfare.
She was wrongfully brought to the UK by her mother in September and a family court judge in Melbourne had ordered her return to Australia.
Mr Uhd is Australian, Ms McKay was born in Birmingham but had been living in Australia for more than 20 years, and Ruby was born in Australia, lawyers say.
The case had been analysed at private hearings but Mr Justice Keehan lifted an identity bar in the hope that publicity would help find the youngster and her mother.
He also authorised the publication of photographs.
Lawyers representing Ruby's father had asked the judge to allow the girl's disappearance to be revealed.
They said all other efforts to trace her and Ms McKay have so far failed.
Lawyer James Netto, who is also representing Mr Uhd and is based at London law firm Dawson Cornwell, said Ms McKay and Ruby are thought to be living in a blue Renault Trafic camper van, registration E527 HPC.
He said Ms McKay has one relative in Birmingham and others in the Littlehampton area of West Sussex.
Mr Netto said she had also spoken of possibly travelling to Scotland.
He said Ms McKay, who also uses the surnames Booty and Garrick, is a qualified yoga teacher and veterinary nurse.
Ms McKay and Ruby might be living on campsites, caravan parks or farms, Mr Netto added.