PAX hands over lost and found items to the venues where an item is found. If you've lost something, make sure to check with the Convention Center and any of your hotels you may have been staying with, depending on where you think you lost your item.The main PAX building venues:
Washington State Convention Center
Grand Hyatt Seattle
Sheraton Seattle Hotel
Hyatt at Olive 8
You can post about your lost/found items here, but one of those establishments will likely have a better chance of finding it.
I hope that all lost items are found by their owners!