First off, if you have the address, I don't think you need to know what ward the moved to. I believe the option appears in the chance that they have moved into a singles or language unit. While the system will accept new unit, I don't think that's required.
As for finding where the people have moved to, you may want to read the First Presidency letter, 29 October 2012: Finding Lost Members. It lists the required steps.
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