Trying to find new people that want to do exactly what you do is next to impossible in-game. I suggest that there could be a sort of craigslist-like billboard in the Tower where people could post what they want to do and with what type of people etc. For example, someone who wants to join a Raid group could post their stats/info and when they want to do it so that a Raid group that needs one more person could invite them. Just one example but I think this could really help the social aspect.