I agree with Mo_Bowhnter.

Either you need a larger target or you should get closer to the target. I on occasion loose an arrow(knock on wood) it's been a while but the surefire way is to keep them on target. If you've lost a couple and you know about where they are I suggest getting a butter knife If you were shooting in a North to south direction get about where you expect the arrows to be. Insrt the knife into the grass and cut in a east to west pattern. If you hit something don't cut harder! Investigate.

It can be time consuming but it should pay off, Espically if there are a few arrows in the area.

Good Luck