We are here to rescue you! If you have an address you'll be able to locate the APN number in an instant! 

Enter the address in the search widget. This action will take you to the "Property view" click on the first tab labeled "Property Records" below "Property Ownership" sub-header you'll see the APN

On the other hand: If you are a Pro or Premium user, you can search by APN. Choose the "Search by APN" option and the search widget will come up. Fill up the APN field,  since APN's are formatted differently, you may just enter it as you have it (including spaces, comas, dots, etc) the APN free form will "format it" and search it, as long as you know the county and the state, a result should come up