A former customer service officer was jailed for 30 months on Tuesday for having sex with a 15-year-old girl.

Chee Wei Tong, 24, who faced 10 charges, had admitted to three counts of underage sex at his Kang Ching Road flat and at a staircase landing of an HDB block in August 2012.

Chee, who was a grassroots volunteer at Punggol 21 community centre, is the fourth man to have been convicted and jailed for having sex with the girl. His sentence is the stiffest to date.

The court heard that Chee came to know the girl in mid-2012 when she created an account on OkCupid, a dating and social networking website.

In the course of texting, she told him she was only 15 years old. He told her that he had a girlfriend and practised polyamory - the philosophy of being romantically involved with multiple individuals at the same time.

He also told her that he had a fetish for bondage and discipline, dominance and submission, sadism and masochism, and encouraged the girl, then a virgin, to read up on this group of erotic practices, called BDSM in short. She complied.

The girl turned up at his home on Aug 1, 2012 when he had sex with her for the first time. He also had kinky sex with her by slapping her face and buttocks a number of times and choking her lightly.

During the second week, she went to his home where she performed oral sex on him.

They met a third and final time between end-August and early September the same year when he took her to an HDB block in Punggol for sexual activities.

District Judge Hamidah Ibrahim noted that the girl went on to have sex with four other men after Chee. She agreed with the prosecution that Chee had morally corrupted the girl.

She also agreed with the prosecution that there had been aggravating factors. Deputy Public Prosecutor Sharmila Sripathy-Shanaz had said Chee treated the minor as a sexual plaything and had to be held accountable for his base, irresponsible and illicit actions.

Chee, who is married, could have been jailed for up to 10 years and/or fined on each charge of having sex with a person aged below 16 years old.