1. Your tracking is this:
Number: LK003985088CN
Package Status: In Transit
Destination Country: United States
2016-09-13 01:11 CHINA, SHANGHAI EMS, Processed Through Facility, Your item has been processed through a facility in SHANGHAI EMS, CHINA at 1:11 am on September 13, 2016.
2016-09-12 14:02 Origin Post is Preparing Shipment
2016-09-12 14:02 CHINA, Acceptance
Origin Country: China
2016-09-13 03:48 In Shanghai, left Shanghai Pudong airport
2016-09-13 03:48 Shanghai City and leave Shanghai to Chicago
2016-09-12 14:02 Shanghai, Xujiahui (this part) has been received (the embrace cast member name: Xu Yang, Tel: 18918381081)

2. I also found this:
International Mail# LK003985088CN Tracking Result
Summary
Tracking number Origin Destination Status
LK003985088CN CHINA UNITED STATES On route

History Detail
Local date/time Activity Location Remarks
12-Sep-2016 14:02 Received by Post Office 200030
13-Sep-2016 01:11 Departure export customs SHANGHAI EMS

3. So according to the above tracking your parcel is On Route to USA. I don't see any problem about your parcel from departing China. The only problem I could see is in Chicago Inbound warehouse, there might be to many parcels arriving and the waiting time for the Customs Officer to inspect the parcel is longer.

4. I would say give it another week and if you don't see any new tracking on the USPS site, then contact seller and tell him of your situation about the parcel.

Hope this help.