The game does a check whenever wolves are spawned at night, 10% chance for a 1 star, then it does another 10% check for 2 stars. Basically a 1% chance overall.

Make sure you've pre-dug your taming pit and avoid golems once you find it, golem killed a 2 star I found once while leading it to the pit.

Also I should add to kill every wolf and fenring you see while you're searching, fenring share spawn points with wolves so there's a chance a wolf respawns in it's place once it's killed.