A 24-year-old Colonie man who used Facebook to meet hundreds of teenage girls was sentenced Thursday to 13 years in state prison for raping four of the victims in his home.

David Bradt pleaded guilty in January to four counts of third-degree rape for having sex with the underage victims — ages 15 and 16 — in his Maplewood Avenue home between July 2 and Oct. 10. His plea deal called for between 12 and 13 years in prison.

On Thursday, Judge Thomas Breslin opted for the 13-year stretch and 10 years post-release supervision.

Bradt, who did not speak at his sentencing, used Facebook to meet more than 700 girls, mostly between the ages of 15 and 20. He appeared on the social networking site displaying a tattooed bare chest and underwear above low-slung pants.

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Bradt began by “”friending”” one teenager on Facebook — then “”friended”” all of that girl’s friends. He continued to stockpile “”friends”” in what police and prosecutors described as a pyramid-type scheme.

After the sentencing, Albany County District Attorney David Soares told reporters Bradt targeted high-school cliques and exploited them.

“”When he was ‘friending’ one girl and he was able to see her list of friends, he was basically using those girls as leads, like you would in a business,”” Soares said, joined by Assistant District Attorney Shannon Sarfoh. “”That’s how he was venturing into these other networks and was able to identify and find all of his prey.””

Colonie police arrested Bradt on Oct. 16 after the mother of a 16-year-old girl became concerned over unusual text messages her daughter received from an older man. Although her daughter was not victimized, she called police, which led them to Bradt.

At the time of the arrest, investigators found Bradt’s desktop computer displaying a MapQuest website with directions to a Glenville home for a meeting with another underage girl.

“”If it was not for a parent who was paying attention,”” Soares said of the woman who tipped off police, “”I would have hate to see what this person would have done if left unattended, unmonitored and unchecked.””

While Bradt pleaded guilty to four rapes, his victims numbered about 20, Soares said.

The plea deal did not prevent Bradt from facing new charges should additional allegations arise. He waived his right to appeal.