Yes it so damn frustrating when you cannot find memebers!!
What is more so, is when you find someone and they change anything and are lost once again because they do not tell you!
I have used many seach engines for addresses?phone #'s. The only way after that is to get on the phone and call or send e-m's.
Check with the Alumni Office at your School, or your Organization to see if they have a data base.
As impatient as I get, I call. Phone bill was not cheap, but found many, who gave me others, who gave me others!
Never give up as I do sometimes, but I suck it up and keep after it! It pays off when your old Alums come back for a function!