If the letter containing the gift card did not arrive at the destination address, you could report the missing letter and gift card to the local Post Office branch which handles mail for your ZIP code. Take the store receipt for the gift card along and ask the Post Office Branch manager what the Post Office can do for you in this situation.
You could report the incident to the investigative department who handles these types of cases for the United States Postal Service (USPS). A formal complaint can be filed with the U.S. Postal Inspection Service to report an incident of suspected mail theft.
https://postalinspectors.uspis.gov/inves...
The USPS Office of Inspector General also accepts complaints. You can use their online form, write a letter, or just call the Hot Line toll-free number.
https://www.uspsoig.gov/hotline
While reporting the crime may not get back your investment into the missing gift card, it might be enough to start an investigation with the result of catching and convicting the thief. No proof, but a news story on the internet did mention that USPS will only cover a maximum of $15 dollars on an insured gift card, no matter the higher face value.
http://boston.cbslocal.com/2014/02/03/ma...
http://legaltimes.typepad.com/blt/2012/12/in-mail-theft-sting-postal-service-uses-electronic-tracking-device.html
http://www.dispatch.com/content/stories/local/2013/05/31/columbus-mail-carrier-faces-theft-charges.html
that why you should insure items of valuable plus you could sent pritoy with tracking
Not unless you sent it insured.
If you have proper documents you can submit it the higher authority to find out it.