I am a huge fan of the Super Nintendo cult classic EarthBound. (For the uninitiated, it's a classic video game RPG but set in the modern day. And it's quirky as hell.) The game is pretty heavily spoiled, but if you want to play it with no prior knowledge, know that spoilers are ahead.
Paula is unique among the player characters, being the only one with the ability to Pray. This weird little idiosyncratic ability allows her to cause random status effects, and is generally a dangerous tactic — some of the effects restore HP to the party, while others put everyone to sleep, ally and enemy alike. One even revives everyone in the battle, reviving fallen party members and enemies.
However, in the final battle against Giygas, Paula has to use the Pray command to draw on the strength of everyone they have met in their journey. The combined psychic weight of the people of Earth banishes the eldritch alien.
A Game Master would have to severely limit its use, but a cleric could easily have a Pray power as described above. When the PCs are aware they are entering a tough battle, they can prepare using the Pray power. Once used, the GM could post on any social media he or she uses, attempting to garner support. ("Hey, my PCs are descending into the Demonweb Pits tonight. Show your support for them, would you please?") Each "Like," "Comment," "+1," "Share," or whatever show of support your local social media site uses counts for something.
That's about as far as I've gotten with it.
My thought was that each "+1" or whatever gives a floating point in a pool (we'll unimaginatively call it "the Prayer Pool"). Points in the pool can be used to increase die roll results for one roll, temporarily increase HP or defenses, or possibly diminish enemy dice roll results. Once the pool is depleted, that's it, so make sure it counts.
The Pray power would have to be heavily curtailed — maybe it's usable only once per level, or adventure, or even once per year. If you play the sort of game where this sort of thing wouldn't seem heavy-handed, perhaps it's only usable by GM fiat.