Jobs at small Detroit companies nobody posts about - what worked for you?

Two small Detroit employers told me they are hiring but have not posted yet. There are 5 people counting on me, so I am trying to be careful. One is a print shop, one is an accounting firm and one is a clinic. Should I visit in person?

A short email with two sentences about what you can do and your résumé attached worked for me. I followed up after a week.