I always draw my characters, and if they aren't fun to draw, then they're not fun to write about (for me, personally). I'm also really specific about what they look like, if not in the text than in my own head. XD It's really hard for me to find celebrities or models that match up, because I try to keep my characters pretty average in the looks department and let's be honest, celebrities are usually the cream of the crop when it comes to attractiveness. I prefer Average Joe types. Model Mayhem is a great resource for people searching for "look alikes", since there's such a wide range of appearances (plus you can specify race, eye color, hair color, weight, etc). It's also good for drawing references!
I also like to draw characters for my audience, because I want them to imagine them at least in a similar way as I do. For example, it's pretty common that people assume the characters are white unless stated otherwise. Hence why I drew this book cover:
For this, I used actual fashion models (Dominique Hollington) since the younger men are supposed to be really attractive, but the lower one was based on a picture I found on Model Mayhem, since he's supposed to be older and average. He kinda ended up hotter than he should have been. >_> Of course, now that I've used these references, this image is canon, and later I described my characters with these guys in mind. It's kind of a chicken-and-the-egg argument, because I don't know if the character description is based on the reference or if the reference is based on the character description.