After three days of scouring bushland north of Brisbane, police believe they have found the remains of missing 22-year-old Samuel Thompson.

The discovery follows murder charges laid against two men, including anti-Islamic State fighter Ashley Dyball.

Detective Inspector Tim Trezise said dog squad officers found "a grave site" on Monday morning about 300 metres into Beerburrum State Forest at Caboolture, about 50 kilometres north of Brisbane.

"Whilst it is too early to say whether this is connected to Sam's disappearance, we're optimistic that it may in fact be Sam's body," he said.