OP, you can file a complaint with the post office's inspectors, and they will do an investigation. Not sure if it will accomplish anything toward getting your package back, but if your letter carrier has been on the lazy side of getting packages to you, it might convince them to follow the rules for a while, and not be so lazy.
Like others have said, insurance is your best bet in the future. It's cheap, and it keeps the packages from getting "lost" so often, and you're covered if they do. One tip: insure it for over $50 (where they actually fill out an insurance slip and put a blue & white label on the package), and it will require a signature upon delivery (under $50 just gets stamped "INSURED" on the package, and no signature is required).
My letter carrier at my old address had a bad habit where, if he had a package that was barely too big to fit in the mailbox, instead of taking it up and leaving it by the front door (which would have meant turning his vehicle off, taking off his seat belt, walking 60' to my door, dropping the package there, then reversing the steps he took to get there), he would flip the mail box door down, put the package on top of it, then put a rubber band from the hook on top of the box, to the hook on the door. Gee.....nice way to leave a package out where it's really easy to steal!! :awe:
And they did get stolen, once or twice!! D: