What do I do if I don't know my landlords address?

Call and ask him, kindly text him or one of his relatives using a google search, use his last name to look up a county tax record, find him on facebook or similar, read lease agreement, ask property manager, ask neighbors to the house your leasing,  ..........hope that helps..im probably missing a few more things...im a landlord and I would make certain you have it. Sorry thats happened to you.

Use whatever address you would send your rent payments to.

Look up the tax record for your address, that has the address of the owner listed. 

If you are unsure how to do that, ask at your city hall.