POLICE were last night hunting for a man who has gone on the run with his 14-year-old cousin after they started a relationship.

Detectives are treating the disappearance of schoolgirl Margaret O'Brien as abduction.

It is thought the pair were heading for Scotland, but alerts have also been sent out to ports and airports after it emerged the teenager had taken her passport.

Margaret went missing from her home in Thornaby, Teesside, on Good Friday, with her 23-year-old cousin, whose name has not been released.

Her parents last night appealed for her to get in touch.

Her mother, Catherine, said: "All we want is for Margaret to come back home. She will not get into trouble, all we want is for her to be back here with us safe and sound."

Police said the schoolgirl had gone off voluntarily with the man.

But they said Margaret's disappearance was being treated as child abduction because she was taken from the custody of her parents.

Detective Superintendent Shane Sellars, of Stockton CID, who is leading the investigation, said: "She is vulnerable because of her age, and it is important Margaret makes contact with us or her family as soon as possible.

"If her family or friends know of her whereabouts, then they should contact us as soon as possible."

Police confirmed that Margaret was in a relationship with the older man but said it was not clear how intimate it had become.

Det Supt Sellars told The Northern Echo: "We know that a relationship has developed between the pair over a period of time.

"We think that he has been in contact with her for the past 12 months, but it's not possible to say how far it has gone.

"We are taking this very seriously because, at the end of the day, we're talking about a 14-year-old girl.

"The fact is she is young and impressionable, and it is very important we find where she has gone."

Police said there had been rows in the household because of the relationship with the older man, who has been working abroad.

Police yesterday declined to name the man, who is thought to be Irish, for what they described as operational reasons, but appealed for the public to be vigilant.

At the family home in Vulcan Way, yesterday, a woman who answered the door declined to comment.

A neighbour said: "Margaret is a pleasant, chatty girl. She is very pretty and close to her mum. Catherine will be extremely worried."

Margaret walked out of the house at 8.30am on Friday without telling her mother where she was going.

She is described as having long dark hair, blue eyes, and is 5ft 4in tall.

She was last seen wearing a pink bomber jacket, blue jeans and high-heeled boots.

She was also wearing gold-hooped earrings and a distinctive necklace with a diamante letter M on it.

Det Supt Sellers said it was thought the couple were heading for Scotland because the man is believed to have relatives there.

He said: "That is our major line of inquiry at present.

"But since Margaret has her passport with her, they could be intending to go to anywhere.

"They may be planning to go to Ireland or mainland Europe - we just don't know at present."

Anyone with information about Margaret is asked to call Cleveland Police on (01642) 302387, or Crimestoppers on 0800 555111.