Mohammad Arshad, 35, trawled through Facebook to befriend girls before grooming them and encouraging them to meet him.
He would cruise around Luton in his Mercedes with his carefully selected victims wearing his black police shirt and trousers.
He would beg all his victims for sex and raped one 14-year-old girl on the back seat of his car.
He was serving as a trainee officer for Bedfordshire Police at the time but was immediately suspended after one of his victims came forward.
It was discovered he had contacted his victims over Facebook, Blackberry Messenger, WhatsApp or texts, St Albans Crown Court was told.
Prosecutor James Newton-Price told a jury of six men and six women: “He flattered girls and complimented them and sent sexually suggestive messages.
“Some of the girls liked the attention and may have been flattered, but if they are under 16 it doesn’t matter.
“Most refused his sexual advances. Some thought it was a joke.
“He persistently pestered girls for sex or some sort of touching or groping.”
Bedfordshire Police launched an investigation and searched his home in Luton, Beds., where they found dozens of images of teenage girls on his phone and computers.
The court was told how the youngest of Arshad’s victims was 13.
He paid one 16-year-old for sex – something that was illegal as she was aged under 18.
Arshad, of Ferndale Road, Luton, denied 22 charges against 13 girls, including rape, between April 2014 and October 2014 but was found guilty of 17 sexual offences at St Albans Crown Court on Wednesday (March 9).
The convictions related to 12 of the girls.
Arshad, was found guilty of rape, nine counts of causing a child to engage in sexual activity, three counts of sexual activity with a child and two counts of meeting a child following sexual grooming.