Identify yourself and your connection. You will not receive replies from even a quarter of the recipients, but those you do get can pay off handsomely. Once you've exhausted the leads from this list, spread your search over a wider area.
P lacing a letter to the editor request for information can be quite helpful .
Two letters in two papers in two states yielded four correspondents and much useful information for me a few years ago. All were in some way connected to at least one of the names I listed in my letters. One was even hostile and rejected my requests, yet I was still able to glean from her brief note some information and the happy fact that a family tree had been completed. This I later found online and as part of a genealogy programme's CD collection of family trees. I may not have looked otherwise.