Robert Morrison, of Glennifer Drive, told the youngster, who can’t be named for legal reasons, that he would grab her from behind when she was alone.

He went on trial over the comments, claiming they had been sent from a copycat account mimicking the bogus ones he’d set up.

Eamonn McGeehan, defending, made a no case to answer submission, saying that even though Morrison had confessed to police what he’d done there was no evidence to say the comments had been sent from the Facebook profiles he created.

But Sheriff Tom McCartney ruled Morrison was responsible and this week found him guilty of making offensive comments to the youngster through the popular social networking site back in 2012.

Morrison told officers probing his comments that he made them after falling out with the girl. Paisley Sheriff Court heard that the former Barrhead High School pupil set up pages in the names of American porn stars Paige Turnah and Faye Reagan.

He used the bogus profiles to start chatting to girls and the chats he had with the youngsters, who were just 14 at the time, quickly turned sexual. When their racy conversations dried up Morrison threatened to rape one of the girls he was messaging.

Morrison, who is now 19, denied sending obscene messages to the girls between May 3 and 10, 2012. The police were contacted and Morrison’s home, in the Cross Stobs area of Barrhead, was raided by police.

A Lenovo laptop was seized from Morrison’s bedroom, a Dell tower PC was taken from another bedroom in the house and the then 17-year-old was taken in for questioning.

He declined his right to speak to a solicitor before he was interviewed and, during the interview, he admitted he’d threatened to rape two girls.

When asked if he had been involved in a sexual conversation with one of the girls and had fallen out with her, he replied: “I think I just started to threaten her sexually. I was just saying what I said before - that I would just kinda meet up with her.

“I think I must have said I would rape her but I can’t remember that well.” During the interview he said he got angry with another girl as well and made similar threats.

He said at the time: “I said I would meet up with her and attack her on her own.

“Just attack her and surprise her, if she didn’t see me coming, from behind.” He told the officers he knew who Faye Reagan and Paige Turnah were from visiting porn sites online and admitted he’d set up the fake Facebook pages for the actresses.

The girl Morrison threatened to attack in the street gave evidence from behind a screen so she did not have to see him.

She told the court her pal was “worried and a bit scared” after receiving a rape threat through the site.

A police computer expert said it was possible to impersonate others on Facebook — after saying that a test he’d done on Morrison’s computers did not prove he’d sent the girls the messages.

But Morrison was convicted of sending offensive internet messages to one of the girls and sentence was deferred for reports. He will learn his fate when he returns to the dock next month.