Get there phone number.
Goto
www.craigslist.comGo under FREE, Post an ad using an alternate email address, stating you have a free guitar with amp, first person to call gets it.
Throw there phone number up there.
Last time I did that my friend got 200+ phone calls, 150 voice mails, 190 text messages.
Make sure you select the option of hiding your email address. You'll be golden.
If they have a truck or SUV, or a car with decent ground clearance, get a box and write in big bold letters FREE KITTENS on it, tie it to the back of there bumper, and hide the box under the car. They won't see it when they go out to the car, but when they drive it will drag behind. People get PISSED.
Or if they drive a EDIT: Small convertable like I would assume, throw some baby powder or pepper spray in the AC Vents next time they leave there top down.
Like someone said earlier, throw off there power sometimes.
Take out a license plate light or two, they'll get pulled over within a week.
I got tons more.