I'll cosign all these findings because they correlate exactly to my own experience. It's the tragedy of the 21st century that we happily nuked existing social structures in favor of a "build your own social network" mentality that it turns out doesn't work that well.
I've never had the experience of being accepted socially in these so-called social structures. My parents went to church and forced me to go. I've generally worked, and had school and stuff. It is nearly too bad I don't believe in God enough to withstand such things. I might as well been invisible at school, and I only rarely have made any sort of friendship at a workplace that carried over outside of work. Living away from family has been normal, and sometimes would go a few months in between visits due to money issues. I'm the weird one in the family - my brother in law said I was the weirdest person he'd ever met... until he met my spouse.
However, I have met friends online that I have kept for years. I interact with folks that aren't turned off by my weirdness. Met my spouse over the internet, and talking to him, though overseas, eased loneliness. The same lack of extensive social network at home allowed me to more easily move overseas when we married. Oddly, being an immigrant has made my weirdness easier and people tend to be a bit more accepting (minus the anti-immigrant folks).
Is there evidence that this actually happened?
At least in America, I think the forces of social atomization predate the rise of social networks. The classic "Bowling Alone" was published in 2000, and it was an expanded version of a 1995 essay.
If anything, I expect that the Internet is helping. I left my home town (pop 200k) because my professional and cultural interests were too esoteric. Now I know know youngsters in towns of 500 that have an encyclopedic knowledge of anime. I see technologists working from anywhere and everywhere. Some will use that to rove, but I know many use that to stay close to family and friends.
And personally, the on-line social networks are how I arrange a lot of my meatspace social time. There are a lot of people I am now back in touch with that would have been lost to me without social networks. That isn't to deny the points of the article, which I agree with. But as much as Facebook irritates me, I don't think I can blame it for this.
At least geeks have the Net though. Huge portions of the population have no genuine social group as they get older. It is no wonder the Japanese are obsessed with high school. It's the last time their peer group was together. Things like participation in sports, religion and other quasi-social affairs are in decline.
Social networks actually have the potential to help restore local social structures as at root they are about connectivity. A local volunteering group can easily keep its members up-to-date via its FB group. A local Councillor can update his constituents via his Twitter account. I'd like to see a new batch of startups which work on channelling social media usage to properly social ends.