Maladaptive Daydreaming: where wild minds come to rest
I wish I was creative enough to envision people I've never seen before, but usually I imagine my characters as actors that I can put a face to. However, that's just for visual reference. Their characterization is usually different from whatever movie/show I've seen them in (unless my DD trigger is a TV show I'm watching).
There are a set of 1-4 close people in my life that I will insert into my daydreams. Like Ivy says, since it's a different setting, they aren't always themselves, but they do always carry the traits that I most identify them with in real life.
I have a few fake characters, like recently I've made the character "April" from "Chasing Life" on ABC family my best friend in real life. I also use people from real life though. And sometimes I just totally make up people.
honestly, for me it's somewhere in between. I'll use my favorite celebrities names and faces, but only just a bit of their personality. occasionally I'll daydream about people in real life, but quite rarely.