The rules for service must be followed even when you don't know where a respondent may be located. In your particular case, this may involve attempting service at his last known address, followed by service by publication. There are very particular rules that must be followed. From the sounds of it, you may have grounds to petition for a modification of the placement order as well as for contempt for non-payment/under-payment of support.
You should contact a family law attorney practicing in your area.
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