If the tracking for your order indicates it delivered but you are unable to find it, please contact USPS via one of the options on this page for help in locating your package:
We do not cover replacement for packages which are stolen from your property, or packages which are delivered to an address you may have incorrectly entered in your order. We cannot be held responsible for the security of an unattended mailbox, porch, doorstep, etc. - we are only responsible for getting it delivered to your postal address.
That being said, package theft is a very real and increasingly common problem these days with ubiquitous online mail order.
If you believe a package has been stolen you are advised to file a police report as well as place a claim with your credit card company or bank, as many credit cards do cover theft with proper documentation.
In rare cases where USPS does indeed "lose" your package, or deliver it to the incorrect address, it is often insured through our commercial relationship and we are able to cover a replacement.