There are faeries pretending to be Elvis, Hitler, and Marilyn, feeding off the energy created by their "sightings."
To give some examples of how comics might create faeries, there is a story Alan Moore tells of how he was in a bar and met John Constantine, a fictional character that Moore himself created. Moore also claims to have bumped into Constantine once previously. Moore seems to tell these stories in all seriousness.
A fictional example would be in the film ADVENTURES IN BABYSITTING, when a young girl, who is a fan of The Mighty Thor, sees an auto mechanic who physically resembles the character of Thor: long blonde hair, tall and muscular, blue clothing, holding a sledgehammer. The girl is certain the mechanic is really Thor. That's a faerie.
In order for a faerie to get vitality, they have to be interacting with people, and there aren't many stories of people interacting with a "real" Thor, Iron Man, or Captain America. But when the actor playing Captain America dresses up and goes to a cancer ward, acting as Captain America the whole time? That's totally a faerie doing that.
Cosplayers and the Real Life Superhero movement create more possibilities for faeries to gain vitality. When you meet a cosplayer at a bar near the convention, and he looks and talks so much like Thor that he makes a better Thor than the actor playing him? Faerie. Bonus points if he performs small acts of charity, like escorting children across a busy intersection or speaking out in favor of police, firefighters, and other first responders. Real Life Superheroes are faeries who use the superhero story to gain vitality from homeless people to whom they deliver water, clean clothes and bedding, hospital patients they visit, drunken club goers whose bar brawls they defuse, and highway drivers who flat tires they replace by the side of the road. All of these encounters get repeated over and over by the mortals involved, for the rest of their mortal lives, empowering more and more faeries.