just ask them, dont be a stalker. if it's not listed somewhere on google, they probably dont want you contacting them. that is unless there someone you cant meet physically...but then theres other means like passing your name down the grapevine, or chatrooms/messageboards like these.
you could also try facebook/myspace/freindster etc if the person you're looking for is under around 25 (there are older exeptions) or is a popular public figure among young people (artist/entertainer/author/politician).