when you throw a spear like this, mark your location on the map. then, look in the direction you think you threw it, and put markers in a line on the map. comb back and forth in this area.

you have 2 in-game days until it despawns.

if you think you know the general area, build workstations, which will prevent item despawning.

remember that in the mistlands there are a lot of slopes, so the spear can land somewhere and then slide downhill, far away from "the line" you made on the map.

you can also make a flint spear and try to "recreate" the throw to get an estimate on where the other one could have landed.

place whisp lights to remove fog in the areas you search.

make sure to turn on auto pickup.

if you are really desperate, consider smashing the stone obelisks to flatten terrain.

no spear left behind.