How do I file a tracer with the USPS?

A tracer is the formal way to request a package investigation with the USPS. The USPS will usually provide you with written documentation of their findings. You can call the USPS at (800) 275-8777. Specifically, call (800) 275-8777, Press "6", Press "4", Say "More Information", then once you reach someone request documentation of your issue. More details can be found here.