Before social media, those are people we forgot about and moved on from. And for good reason.
Social media, especially Facebook, seems engineered to create this illusion that we're more connected with our "friends"; while those people may have been our friends in another time, that doesn't mean they're our friends now just because we have Facebook connections with them. If it only takes not having a Facebook profile to not exist to people, they're not really our friends to begin with. I can say this about the vast majority of people who are my "friends" on Facebook; I know for sure that 99% of them will never contact me unless Facebook prods them to post "Happy Birthday" on my timeline. This isn't to say that my connections are bad people, but it's to say that social media has distorted what friendship and human bonding actually mean in order to profit on peoples' loneliness.
It's not difficult for a truly lonely person to come to that conclusion, but that perspective solidified in me when I became real-life friends with a neighbor of mine. It had been several years since I made a non-superficial friendship. And no social medium was required. I was reminded that real friends are actually interested in seeing you, talking to you, and coming to you first when they've got news about something. Just one friend like that is far more valuable than all the "friends" I ever had on Facebook.
You may still feel a void from it, but I do hope you eventually make some real-life connections like I have and forget about your old "friends" entirely. I abstained from Facebook for 9 months, and even near the end I was feeling the void. Going back to it was starkly different and I realized how much of a waste of time it is. I do still use Facebook, but only as a photo repository since I do have some semblance of friends and family on there. Though I'm sure they wouldn't bother with me if I wasn't there to bolster their friend-count.