It's really frustrating when package get's stuck In Transit. You can try asking the seller to go to the USPS site and file "where is my mail" claim. You may have to do it 2-3 times - the tracking is showing "Moving to the next facility" for 3-5 days - that's the time to file a claim. Give it about 3 days, and the chances are they will find your package. If it doesn't help the seller need to contact the customer support.
Try submit a missing mail request, first, sometimes it may get the package moving again. It is not unusual for some delay even for Priority Mail, especially during these times.
If you brought your shipping label through Etsy, then for Priority Mail it is automatically insured up to $100. You can file a insurance claim for the lost/missing mail for Priority Mail after 15 days, but no later than 60 days. I would wait a bit more though before filing for insurance considering we're still in a pandemic as of February 2011.