For Sherri, as soon as I held her I asked the girl (a.k.a. my best friend/brain twin/one-on-one RP partner) "who looks like she could be Daisy Lowe's sister?" and she responded very quickly with "Lily Allen." I wasn't sure on her at first because, although I love her music to an insane extent, her personality seemed to be totally off for someone I could picture as the character I was coming up with. Flipping between pictures of them convinced me, though, and I was able to find enough pictures that would work that I was comfortable with going with her!
...I'm honestly not completely sure how I came up with Zachary Levi for Theo. I'm blaming the fact that I was trying to catch up on Chuck at the time, and my PB browsing didn't reveal anybody who wore a lot of hats anyway. In hindsight, it was totally a good call and it'd be hard to find someone else as quirky and awkward as Zachary Levi.
As for Miss Moana, when I first started eying the premade before Pax opened I had a brief thought of using Skin from Skunk Anansie because I have wanted to use her as a PB for a long time. And then I laughed at myself and decided on Angel Fershgenet Melaku Lola Luv or whatever she's going by this week who I'd also been eying and wishing for a chance to use and who I knew was perfect in ways that I cannot even begin to express. As far as Skin goes, maybe someday I'll find a role for her (she'd be a great Erzulie Dantor but that is one vodou lwa I would not want to offend).