Ashley Skinner, seven, hasn’t been seen for four years by his father Michael Turberville.
He is believed to have been taken to Australia last year by his mother Joanne Skinner, a trade union worker.
The President of the High Court’s Family Division has taken the unusual step of lifting the reporting restrictions that apply in children’s cases in the hope that publicity will help trace the boy.
Sir Mark Potter said: “This is a boy who has been snatched by his mother during court proceedings intended to decide how much contact he should have with his father.
“This mother’s behaviour is to be deplored. She has gone to extreme lengths to go to ground with Ashley and to cover her trail so as to avoid detection. It seems she has taken, and will continue to take, every opportunity to defeat the court process.
“As a result, Ashley is being deprived of a relationship with his father.”
Mr Turberville has spoken of his despair at missing vital years of his son’s life.
The 41-year- old, who lives in Reading, Berkshire, advertised in the Pink Paper for a woman with whom he could have a child.
Both were in relationships with same-sex partners when they decided to embark on parenthood. They tried home insemination nine times before they succeeded.
Mr Turberville said the arrangement has worked well for three years following Ashley’s birth, although he had been puzzled that Miss Skinner refused to put his name on the birth certificate.
“I saw him about every other weekend or when she needed me to babysit,” he said.
He said Miss Skinner has asked for a break in contact as she dealt with a difficult break-up with her partner but that subsequent attempts to re-establish a link with his son were rejected.
Miss Skinner responded by making criminal allegations against Mr Turberville — unconnected with Ashley — of which he was acquitted by a jury and exonerated by the family court in September last year.
He said: “The last time I saw him we had a little birthday celebration in a local park and we were happy. Then just after his third birthday Joanne and I were talking and she suddenly said ‘I don’t know what you are concerned about, you have no say in the matter’.”
A series of court orders aimed at tracing Miss Skinner has met with no success and there is evidence that she fled abroad without returning to the UK.
Mr Turberville added: “I’ve missed so much, his fourth, fifth, sixth and seventh birthdays, riding his first bicycle, his first day at school. I’m devastated to have missed these things.”