Boars find you. My favorite method of finding boars is to run to exhaustion, at which point I inevitably run into a ** heard.

Seriously, do everything else you need to do. When you wander into a boar's threat radius, they let you know.

You can also listen for them. One sound they make is quite subtle, it's just an exhalation, like "ha!," not very loud. Wear headphones. As you play, you will learn to recognize the shape of a boar from pretty far off.

** Never run to exhaustion. Unless you desperately need to find the most dangerous animal in the biome, with their pals.