I actually prefer using head shots of popular actors or people of people I know/knew.
We do that too. Usually we have some general idea of how a character looks and then we try to find pictures of real people who are as close to what we've envisioned as possible but, well, at least in my case firstly my skills don't allow very good replications of the real people, and secondly we usually change little things here and there (a bigger or smaller nose, different shape eyes, stuff like that).
That's for faces. For bodies we often do try to get as close to some picture as possible. Since we have 18 WIPs and each story has at least 4 MCs and some "bigger" side characters, we've ended up drawing dozens and dozens of pictures and, oddly enough, I've noticed that I'm actually getting better at drawing. Little by little, baby steps and all that jazz but it's nice to look at a drawing I made five years ago and realize I can do better now.
I don't know why but guys are really easy to draw for me (meaning I get them pretty close to what I picture in my mind) whereas I often have to draw a female MC over and over again before I'm satisfied with how she looks. Then again, I find drawing women much more interesting, especially their bodies. Maybe that's because I'm a guy and when I was a kid (like 6-12yo), I drew pretty much just men so I have much more practice with them and being a guy I have a better grasp of the male physique but learning to draw women/girls is, well, fun (even if I cringe when I look at some of my older doodles).
By the way, this reminds me of what a Finnish karateka once said to me: I can't remember what we were talking about but he said that my problem is that I do many things (train martial arts, swim, jog, write, play guitar, drums etc. etc) and I want to be good at all of them. Which has led to me being a (very low-level) jack of all trades but a master of none. I think I've inherited some of my dad's perfectionism and I'm something of a control freak when it comes to my art so my dream is to one day be good enough at drawing that I could draw our characters well enough that the drawings could be published.
Any of you folks have any education in drawing/painting/whatever? I used to go to art classes as a kid and when I was 13-15 I was in a class with emphasis on visual arts. Now I'm just bummed that I didn't draw anything when I was 16-24: if I'd drawn even one picture a day, I would be so much better now. Oh well, at least practicing is fun.