Well, I think I might've lost a Ponytail Petite during moving 14 years ago... Not that I've ever been that much into my Petites, sadly. Also, identifying her is hard, because I honestly can't remember her colors, none of the ones I see pictured online ring any bells, and looking at the ones I have, I have 2 from the 1st set, one from the 2nd and 2 from the 3rd. So I either got two packs with random ponies or I got all three and I lost a LOT more ponies than I thought. o_o I'm betting on the former.
When I was 11, I did lose a pair of Lion King plushies that I'm still sad about, Kissing Nala and Simba. Nala was mine, Simba was my brother's, and we lost them at the same time. X( Though other than (very annoying) exception, luckily I've been pretty careful with my stuff since I was a kid.