Try his family/friends...you'll have to come up with a cover story though (old friend trying to get in touch, etc.)
Also, depending on your state's law, at a certain point after you've made a diligent effort (say like 3 different methods/attempts) to serve the defendant, the judge may allow you to do service by publication (i.e. putting a notice in the paper).
Honestly, though, unless your rent is quite high, I don't see it as worthwhile for only 2 months of rent (isn't your security deposit covering one month?).
If you can get in touch with the guy and offer to compromise (he'll pay a lesser amount) that may be advantageous so that neither you nor he will have to go through the whole asset / wage garnishment thing.
Also, for the future, check if your state has provisions for "distress for rent", which would allow you seize the tenant's property on the premises and sell it for unpaid rent under court order.