I'm sorry you jabe had stuff stolen although at 14 I would not have left a gathering og 14 year olds in my house on thier own. Yes I know you only went to a neighbours and were checking from time to time but all sorts of stuff could have happened when you were not there.
It's a horrible feeling, isn't it? I have had alcohol stolen several times. I have had a camera stolen. I was actually burgled last summer by someone who was almost certainly known to my DS1.
Each time, I had my suspicions about who was responsible, but was not ever sure enough... The first time, I tied myself up in knots trying to be 'fair'. After that, I simply banned anyone I knew who was present in my house when something had gone missing. It was a clear abuse of my hospitality and I decided I didn't need to be 'fair' - I needed to feel that myself and especially my younger DS were safe.
I also had locks fitted on our bedroom doors. We still use them when we're out. This means that I can lock valuables and booze (and in fact tasty treats!) in my bedroom and be sure that they won't go missing.
I hate that I don't trust my DS's friends and acquaintances, but I don't: I never found out who burgled me, and so I have been left with a horrible suspicious paranoia, thinking "Could it have been him, or him?" about several of them.
I wouldn't (necessarily) suggest you fit locks after a one-off incident. You can all put it down to experience. But it is an option, and knowing this might make you feel less powerless... You can't do much, if anything, after you have had things stolen, but you can stop it happening again.
Yes, it was your fault for letting her do this. She obviously isn't mature enough to keep on top of the situation, and that is your fault, not hers. And you cannot accuse someone without proof, the thefts could just as easily have been one of the "lovely" kids that came along
There's nothing you can do, except to learn from experience and limit gatherings in your home to known teens only. I wouldn't stress that much - at least it wasn't on fb so that thousands descended on your home. I had a party aged 15 and will never forget my mum coming home to the chaos and damage; she gave me a hug and said she knew it wasn't my fault!! Why she went out I do not know, but we never had another party.