In some states there are statutes allowing the service of a summons and complaint via a post office box of a defendant as well as the certified mailing of a person who resides out of state or oversees. Most likely your state will allow service of the landlord via a certified mailing of the summons and complaint sent with return receipt.As to the property manager who only has a box at a UPS store, you will have to do a better search for a physical address of the property manager and have him served at that address. There are services that can be purchased online where for a 24 hour period a person can do a search for the location of a person as in your situation.Good luck.