Have you checked for anything of value that might be missing?
We had kids in our house while we were gone once. They made a mess but didn't take anything (just rearranged stuff) It's a real deep feeling of violation.
Try to stay up awhile to assess what might be missing, so you can call authorities at once.
We're not missing anything but we are staying up for a while, primarily because I'm creeped out.
Our first apartment was broken into and I was the first one home and came back to the mess. It felt like far more of a violation than I'd expected, especially because they went through the dresser bureaus and our clothes, etc.
This is probably nothing, but I'm sleeping with some lights on tonight and am trying to talk myself out of locking the bedroom door. LOL
Think I'd better go read a book; maybe Rebecca of Sunnybrook Farms :-) See you tomorrow.