Glen Jeffries, 42, must spend at least 16 months in prison for forcing the teen into prostitution, even when he knew she was under 18.

Following a split from his wife and children, Jeffries met the girl on Facebook in September, 2014 and soon after met her in person to use drugs and begin a sexual relationship, the Victorian County Court heard on Wednesday.

When Jeffries ran out of money for food and rent at his Frankston home, the girl offered to engage in sex work and he escorted her as security, judge Meryl Sexton said.

But later, Jeffries refused the girl's plea she didn't want to meet other men again, and began arranging liaisons at motel rooms in Parkdale, Doveton and Ballarat.

He told the girl his ex-wife and children "would miss out" unless she did so.

Besides standing guard outside rooms, Jeffries also advertised the girl and took some of the money she was paid, the court heard.

The girl claimed she was 18 when she met Jeffries, Judge Sexton said. He later found out her true identity and age but continued as her pimp, and denied to police he knew her whereabouts.

The girl was in Department of Human Services care at the time.

In November 2014, Jeffries met a 13-year-old girl on Facebook and also tried to procure her as a sex worker.

Over the following days, the girl's mother posed online as the 13-year-old and Jeffries was soon arrested.

Judge Sexton said Jeffries' actions had harmed two vulnerable children, and he "did so in order to gain money for your own benefit".

She imposed a two-and-a-half year jail term and ordered the former concreter serve at least 16 months before he began an 18-month good behaviour bond.

The judge said the older girl had been scared during the sex work, felt disgusted and "stripped of her dignity", and still endured nightmares and anxiety around males she didn't know.

"She feels that her body and soul and life have been violated and that it will take a long time before she trusts anybody again," Judge Sexton said.

The girl's willingness to be involved initially was irrelevant, the judge said. 

Police found 15 explicit photographs and a video of the girl on Jeffries' mobile phone, the court heard, but there was no evidence he put the material online.

He pleaded guilty to inducing a child to take part in sex work, possessing child pornography and using a carriage service to procure a person to engage in sex acts.

The court heard Jeffries was at "rock bottom" when he met the girl, and was drinking, out of work and no longer with his family.

But his ex-wife remained supportive, the court heard, and said in a reference he had always provided for her and their children.

Jeffries has already spent seven months in custody.

The story Minimum 16 months jail for man who forced teen into prostitution first appeared in The Age.