I've got it all working (missile spawns and tracks the player, causing damage on hit)
Though it took me a good half hour to discover than when I had aiment set I couldn't see the entity ... this could be because it was set to me so it would be right on top of me, I suppose.
Anywhoo, I'm going to play around and see if I can't make it track people without using 0.1 repeating tasks to change direction.