YoSSI, my truck had a similar problem which is very very easy to fix by yourself with only a phillips screwdriver
That little pin moves becuase it is directly attached to your shifting bar, when you move the bar, you move the little pin. Now, what seems to happen often is that the string that attaches the pin to the shifting bar breaks, all you have to do is take off your dash console cover and you'll instantly see what I mean, just retie the string and use a small peice of wire to reattach it to the little loop that is attached to the shifting bar (not the bar itself by the way, I mean that whole round assembly that moves) Chances are your little pin isn't actually missing, just has been pulled off to the left by the little spring to the point where you cannot see it.
Hope this helps!