How do I locate a previous tenant's job location after he has skipped out?
He left the job that he had when he moved in. He is a plumber and I
have his S/S and driver's license number.

You may want to hire a "skip tracer." These folks specialize in
finding people who have skedaddled to avoid creditors and other
interested parties.

Yes, I know I can hire a skip-tracer. However, I was hoping that you
could be more helpful than merely suggesting what is already common
knowledge.

Just a few thoughts:

1.  Check out www.knowx.com  you can search for professional
licensing.  Can also check for new lawsuits.

2.  Again common knowledge....Ask the neighbors.  I've had several
skip outs and the nieghbors always knew.  You might have better luck
paying one of the teenagers to ask around.