Yayi - too bad this guy is a creep because he's got quite a success rate for grabbing the cats - 3 out of 6 already? Unless they're very friendly, he's got to be using a trap. Do a little reconnaissance and see if you find traps - if you find one, trip it so no cat will get caught. I'd be tempted to take the darn trap and "relocate" it too... (I know, that wouldn't be right but this makes me so angry).
I agree with Hissy that you should try to catch the remaining cats ASAP. This guy is on an evil mission and he won't be happy til they're all gone. I hate to say this but I wonder if this jerk is poisoning them and that's why they're disappearing.
See if you can find a safe place for them to be relocated to - as Hissy suggested, maybe a wooded area. I would try to go through the steps of relocation, though it will be a challenge. You'll have to get a good sized cat cage or carrier and keep them in it for at least 2-3 weeks to get used to their new location. This will only work if you can keep the cage camouflaged - you don't want more cat-haters finding the cats in the cage. If you can't do this, spread lots of dry dog and cat food, as well as catnip in a wide area where you'll be releasing the cats (got this tip from Hissy). They need to associate the new location with their food source, so that may help.
This also means that you'll need to come to the new area to continue to give them food & water, and provide some small shelters for them.
Most important, before you release them, be sure to have them neutered!
If by some chance these cats are friendly, do you have a good no-kill shelter they can go to so they'll have a chance at adoption?
I'm glad you care about these cats - they desperately need a friend! Please don't give up - you can still make an enormous difference to the remaining 3 kitties.