A mate of a Child, Youth and Family youth worker alleges he saw naked images of a young girl on the man's cellphone when it was accidentally left at his house.

The former youth worker, aged 38, is on trial over crown allegations that he had a relationship with a 15-year-old girl who was in care at a Child, Youth and Family (CYF) home where he was working.

The man, who has name suppression, denies charges of having sexual connection with the girl, and meeting her after grooming her for sex, Christchurch Court News website said.

The girl gave evidence yesterday in the Christchurch District Court trial before Judge Michael Crosbie and a jury.

She told of giving the man oral sex at the home, and later having sex with him when he went to Auckland and she ran away from a home she was then staying at.

She also told of taking photographs of herself, undressed, on the accused's cellphone. She said she wrote him two letters and sent them to him at another address.

The man's friend, a former work colleague at another business, said the man told him some letters would arrive from someone in Auckland he was seeing.

He explained he did not want them going to his house because he and his wife were going through a messy break-up.

The man came and collected one letter, but never turned up to collect the second one. When the police asked about the letters, the friend realised he probably still had the second one, and searched for it. He then read it.

The letter was not read out in court. It begins, "Hey Babe."

The friend also said the man left his cellphone behind at his house for about a day after visiting with his children. When he found it, he looked through it.

"I saw images of a young girl. Ones in sexual positions and things like that. She was naked, aged 13 or 14, somewhere around there."

CYF staff members told the court that it was best practice for staff members never to go to the room of one of the young persons in care by themselves. Staff worked in pairs.

They also said it was mentioned in the file of the girl, when she arrived at the home, that she had been sent there because of drug and alcohol issues "and a tendency to seek the company of males significantly older than herself".

Staff told the court that staff members were aware of these issues - "so we know what we are dealing with".

A male staffer told of approaching the accused and asking him whether he had photographs of the girl on his cellphone.

"The reason I brought it up is that it was being spoken about by the young people in the unit at the time."

The accused became rather angry about it, he said.