let me see... Christina Ricci is small and petite, deceptively innocent looking but whether she's pretty or not depends on the person you ask. I think she is but some don't like her.
Kate Hudson is petite, looks like she wouldn't hurt a fly.
Alyson Hannigan is tiny.
Audry Tatou looks very innocent.
Sophie Marceau too.
Bridget Fonda is very petite and looks frail to boot.
Claire Danes, Dominique Swain, Elisha Cuthbert, Emmanuelle Beart, Gabrielle Anwar, Gigi Leung, Heather Graham (not so petite but innocent looking at times), Hsu Chi, Jennifer Ellison, Jordana Brewster, Keri Russell, Kirsten Dunst, Kristin Kruek, Lacey Chabert, Lexa Doig ( she's rather tall but I'm not sure now if you mean petite as in short or petite as in thin ), and that's about it for now...
I can give you a link to a site that has all of them... which is actually how I came up with so many... I just glanced over their listings