Don't know about any online groups. The only piece of advice I can give you is, don't play it in the middle of the night in a one-room wooden cabin in the middle of a dark forest. I speak from experience ;-)
I was on a scouting trip with my patrol. We were about 8 guys, ages 13-15, in a one-room wooden cabin in the middle of a forest. In the evening we started playing Call of Cthulhu. After a couple of hours, our group in the game split up. Since one group obviously couldn't know what the other group was doing, that meant half of us had to go outside until we met up again. That was... creepy ;-)
We huddled outside there, listening to twigs snapping out in the woods, seeing strange shadows moving between the trees, etc. It's amazing what your imagination can conjure up in such a situation.