Hehe, feel your pain, have lost a few spears myself at times; but persistence in searching usually pays off.

Of course it depends on how badly you threw your spear. Accidentally one time threw one up in the air, up in the mountains, where I watched it soar away, then drop, all the way down to get lost into the sea of trees that was the Black Forest below. Finding that sucker was not a fun time. Have to take note of where you were, what direction you threw it in, how far could have it gone... blah blah, then the search. Just when all hope was lost of finding it again, poof, you look at some nook or corner you didn't see before and there it is.

Same principles with plains i suppose. A lot of that grassy terrain can hide stuff pretty well. I do sometimes wonder if thrown spears can get sometimes lost through the terrain a bit tho, same principles of retracing your steps apply. Sometimes coming back to it after an initial search might pop up the spear on the terrain to be seen better...