Look at your in-game map. See those red circles? That is where he will almost always be. Those are his sniping points. You CANNOT run up to those points and find him. You need to hide for a while, then sneak up to one of those points. If he's not at one, try the next closest one. Best done when it's raining, and you can use the rain camo.
I found him to be easiest in the area that has a creek running through it. The creek forms little waterfalls that you can climb up as well. Near this creek is a hollow log. I crawled inside the log, equipped proper camo, had thermal goggles and directional mic handy, and waited. About 10 steps north of this log is one of his sniping points. Since it's almost flush with one side of the area, he always faces west-southwest from this point. It was extremely easy to sneak up on him because I came out of the log almost behind him. Wait until you see him go by (or see footprints with thermal goggles), pop out, shoot, go back in log after he runs, wait a few minutes, repeat.
BTW you can hear him talking with the directional mic. He will say "This...is the end..." and you can also hear him breathing. I only found that useful for ruling out general areas, not for getting a specific drop on him. Example: If I pointed it north and heard him talking, I knew he was in one of the two spots north of me, not the one or two to the west or south.