Your best bet is probably using the in world location search for terms related to the kind of RP you’re looking for and visiting the places with higher traffic numbers to see if they’re what you’re looking for. Note that if you include Adult locations there may be some things you can’t unsee. There are lots of RP locations and groups in SL; more than there seem to be people to keep them busy, so the trick seems to be finding the ones that are active and fun, and that’s mainly just pounding the pavement. My brief experience with groups is that they don’t seem very active and messages are basically broadcast personals but maybe others have had better luck. Best bet is to go where people actually are.