The tracking detail for your package is not available at present. Possible reasons:
1: The carrier hasn't accepted your package yet.
2: The carrier hasn't scanned and entered your package tracking information into their system yet.

I think the sender doesn't sent it out now. He just gave you a tracking number he has on hand.

The sender sent it out on Dec. 23.It's on the way to US now.

Tracking reulst:
2017-01-02 21:23
XI, leaving XI sent to San Francisco

2017-01-01 12:48
Xian, leave sent to Xian XI land transport hubs

2017-01-01 12:48
XI, leaving XI sent to San Francisco

2016-12-23 17:39
Xian, Xian express BA – vote received

Hi,

This package has arrived in your country now. USPS will deliver it to you in the next few days.

2017-01-17 17:16 --SAN FRANCISCO, CA 94128, Arrived at USPS Facility, Your item arrived at our USPS facility in SAN FRANCISCO, CA 94128 on January 17, 2017 at 5:16 pm. The item is currently in transit to the destination.