They say they received a complaint that the 43-year-old was using fake social media profiles on Facebook and the gay dating app Blued to snare his victims.
The soldier would have them send him n-de photos before agreeing to meet the teens.
When the boys found out he did not match his online profile, he would blackmail them into s-x using their nude photos.
Police said in a statement that they discovered medicine for treating HIV when they arrested Sgt. Maj. Jakkrit Khomsing at his home yesterday in the northeastern province of Khon Kaen.
They said tests confirmed he was infected with HIV.
So far they have determined that Jakkrit had more than 70 victims between the ages of 13 and 18.
'Even though the suspect is a soldier, this behavior - and I've consulted with army commanders - is a personal issue, not an organizational one,' police Major General Surachate Hakparn said.
Authorities are widening their investigation and attempting to contact other victims who have not yet filed charges.