I am in my mid 20s, and while I don't think social media like Facebook is irreplaceable, it's damn near that because, without arguing semantics about the word friend, I have friends from all over the world (and even within the same country) who I want to keep in touch with or at least send the occasional, "Hey, how have you been?" Even more importantly, if I end up traveling, it's very easy to keep in touch with them whereas using email is not because they probably get too many emails a day and my email might fall by the wayside and phone is not possible. Beyond this, people change emails and phone numbers all the time, whereas their social media presence doesn't really change all that much.