I'd say it cuts both ways. I don't get out much myself, but I keep pretty well in touch with friends from all walks of life via social media. In another era many of those relationships would have atrophied with both time and distance.
I do it the opposite way actually. No social media at all. I call, text, and email a whole host of people on a regular basis.
Social media is honestly a hindrance of friendships. If you want to know about an old friend you haven't talked to in a while, punch up their facebook/instagram/twitter. All caught up. No need to interact whatsoever. I call, email, and text, to maintain that sense of a personal connection.
Technology helps with having relationships not atrophy, I completely agree. Social media however, I see it as a hindrance to sincere connections with people more than a boon to preserving relationships.
Perhaps. I think people who grew up with social media know it's a loose substitute for maintaining real friendships and relationships. You just won't get the same fulfillment looking at a 'friends' feed than actually reaching out to them directly (via technology or otherwise). Just like you call, email and text - many people do that (snapchat, whatsapp, etc).
I think that would depend on a lot of factors. Some people have more bandwidth for social stuff and can cope with keeping in touch with old friends and also seeking out new ones. Others can't.
But, also, if you are online, you can already know people in the new city. I am somewhat prone to having my friendships start online and then become IRL instead of the other way around. While I am probably not the norm, I am not some bizarre statistical outlier these days either. Plenty of people meet people via Internet and move the relationship to meatspace.