Well.. YOU could read papers. YOU could look up from your phone and notice the flyers.
The possibilities are there. There are other ways to get info about local events than from fb. You don't have to wait for everyone else to pick up a paper.
Ps. I have plenty of friends and involvement, which most of my current social circle I gathered after moving alone to a new city, without using social media. I lost a lot of acquaintances by leaving fb, but none that I actually miss. My friends are the ones I put effort into keeping in touch with.
People exist offline. We've done so for millennia, and still do.
I second the horror/scary movie trope suggestion. PCs being the hunted instead of the hunters means that the DM can keep the pacing tight and not getting derailed, as the enemy will find them wherever they go until they die or escape (or defeat the monster).
If you place them in a contained area where they have explore to find a way out, they can lay traps to slow down (or defeat) the monster, they can find clues as to the monsters strength or weakness, they can try to hide when they hear the monster drawing neat, they can find slightly helpful items (batteries that can be used for a flashlight or in a baby monitor as an early warning system, slippers for better sneaking but worse running, vodka for temporary HP but worse constitution, scissors or letter openers to distract in close combat for a chance to escape) but not straight up weapons, they can take damage to deal damage, or take damage to escape whenever they get found. The monster will let them think they've gotten away but they'll never be safe, it will always find them while they're in this location.
The goal can be survive until sunrise, or try to get as many people out of the haunted house as possible, or survive/beat a set amount of the attractions at a demons fair to be released. It'll be lika a hit+run or cat+mouse game.