The article reports, "On the flipside, groups can extend to five hundred, the acquaintance level," and that would suggest that my group of Facebook friends (a bit more than 700, the great majority of whom I have actually, factually met in person) is a group of acquaintances. And I'm okay with that, as they are FRIENDLY acquaintances, and they interact with one another (in many combinations of individuals who have never face-met even once) in delightful and thought-provoking ways.
I feel a lot of empathy for the younger people commenting in this thread that they feel they have few friends and few channels for meeting any new friends. That may change over time. There have been times in my life when I was much more isolated than I am now, when it would have been unbelievable that I would ever have an online network of 700-some "friends." Of course like a lot of married men, I've invested most in my relationship with my wife, and she is by far my best friend, and also a connection to other friends. I do think the article makes a good point that it's wise for each of us to enjoy some of the in-person aspects of friendship (hearing someone's voice, maybe tapping someone on the shoulder or hugging or whatever as is appropriate for the friendship) to build a connection with people that just can't be built by keystrokes sent over the Internet.