When this issue occurs, (especially around the holidays when delivery drivers are uber busy), give it 24 hours. It is sometimes possible that the carrier marks the package as delivered with plans on delivering it the next day. (I've had this happen to me personally a few times)
You can also take the tracking number provided by us and go to the "Track Your Order" portion of the couriers website and enter it in.
Once that has pulled up the proper information, you can select the tab "Tracking History" and see each location the package has been to. The drivers sometimes leave notes here to, as to where they left the package if it was in an unusual place.
If you are still unable to locate you item, send us a message at firstname.lastname@example.org