Hi, welcome to The Vampire Diaries Fanfiction Wiki! Thanks for your edit to the Caitlin Salvatore page.
Hey Katherine (Can I call you Kath)?
Anyway, I personally use a few websites. As many people who know me know, I worship google!
Therefore, google images is top of my list. Instead of typing in say Rihanna or Tayla Swift, if you want a non famous person type in: "girl with brown hair and blue eyes" or "boy with green hair and purple eyes". Type in the gender, eye color and hair color and it normally works.
The link to google images is here: http://www.google.com/imghp?hl=en&tab=li
Another site I love is: http://www.deviantart.com/
Type in witch girl or vampire boy or whatever you want and it comes up with fantastic art done by people!
Another thing, you can use slightly famous people. But not people like Hannah Montana or Emma Watson/hermione granger. You can use less famous models, however I don't advise singers and actors.