Oh no!!!! I really hope they find it!
My grandmother's bag went missing once. It wasn't at the usual luggage pick up. We went exploring and found some shady guy loading luggage, including hers, onto a cart (he did not appear to work for the airline). We grabbed it so fast and got out of there! I hope your bag is merely lost and not stolen and they find it soon. Did you have luggage tags on it? That would help heaps.
I carry on anything I really care about if I can (i.e. my iPad, purse, pins, etc.) Of course sometimes it can't be helped. I traveled to a horse show and had to put my very expensive riding helmet and boots in my luggage. Hated doing that since helmets are supposed to be replaces after a fall/impact and I was terrified the way they throw luggage the integrity of the helmet would be damaged. >.<
And terrible things can happen to carry ons too, you could get robbed, etc. Heck you could leave your pins safe at home and have a fire or break in. It's impossible to prevent every disaster. Try not to beat yourself up for not taking it as a carry on and putting it in your luggage. Generally luggage is a safe place.
Security is such a crap shoot! I traveled to a and from a place with my backpack, got home to unload it, and discovered I'd accidentally brought my pocket knife!
Didn't even know it was there! Security didn't flag it either time. (Perhaps it was under the length limit?) My hair stick, however, that was questioned.