I you don't know an sober alcoholic I know the best thing you can do.
Go to an open AA meeting or two. Find an alcoholic there who is willing to help your friend by telling him what his (the alcoholic's) drinking life was like, what happened and what his like today. Commonly called a 12 step call.
Meanwhile you can go to AlAnon.
Your heart is in the right place. However you cannot TELL a drinking alcoholic anything. They have more excuses for drinking than you can imagine. I know, I gave them to many people who told me thirty years ago when I was drinking. I was convinced drinking was my solution rather than problem.