My points are this:
a friend is someone you know, knows you and you can count on each other.
Friends know where you live, what your phone number is, what you look like, and that you can be there for them when needed.
All others are a different category.
If you want to know something about someone then ask them. If you have no way to contact them directly then they are not your friends they are simply denizens of the Net, acquaintances, passer bys, fellow hobbyist, maybe even hobby buddies.
So yes, ask them directly their ID's, if that is important, if you cannot contact them directly, then go reach them through their games (see if anyone in their games you have their address) but be prepared for some one to call you out as an Internet Stalker rather than a 'friend in search of friend'.