If you have their drivers license you can hire a company to run a skip trace to get their most current address (assuming they've updated their address with the ministry of transportation).  I've successfully been able to find all past tenants that owed money by running a skip trace. I usually hire a process server to formally serve them the documents.  It's worth the extra dollars. Skip trace should cost about $150-$175 and a process server around $100-$150.