Online Haters: Reply to prove a point or say nothing and have the possibility of looking like the loser?

Im friends with this guy and these girls that don't even know me (they live in a diff city) start talking trash about me on his facebook. They know I can see this, so i made the mistake of retaliating. I wrote something back and they continued to reply as well. I came to the conclusion that they're jealous b/c they like him, so it makes them mad to see pics of me and him posted up on his profile. My guy friend starts to get irritated cause he told them to chill out and me to not reply. So I stopped. A week ped & they're STILL talking crap. ppl say ignore it but I feel like if I don't reply, they'll think that they've won. I want to try a diff approach b/c i hear that replying is "giving them what they want", but it just angers me that little 17 year olds have the nerve to talk so much crap. Although they live far away, it's actually likely that I'll meet them one day. So what should I do? reply, dont reply, or wait til i see 'em in person and beat them up lol jk. help plz! im 20 btw