You should first, if you do not have it already, post "no trespassing/ private property" signs posted around the area. A bow is a dangerous weapon. You SHOULD feel threatened especially when they told you t F off.
Call the cops on them to report the crime and lay it on thick the personal safety concern angle. It sucks that our laws do not extend as far with pets (especially fish), but this is no different than hunters going onto private property without permission with firearms.
There are lengthy prison sentences for these types of crime.
It also sounds like neighborhood kids, if they took off on foot and had no vehicle nearby. You could also print out fliers to the neighbors asking about information of the "left behind bow" so that a agreement may be reached before turning the matter over to the police.
The potential couple hundred dollar potential fine for killing your gar isn't going to motivate the kids or their parents to come clean. The threat of a felony charge might just motivate BOTH, or at least the parent(s) if they bought the bow for their kid(s).
