When I go to the "library" tab at familysearch.org, click on "library catalog" and then on "place search," type in "Muskegon" part of "Michigan," and finally click on "Michigan, Muskegon," I find indexes for probates, vital records including deaths, and cemetery listings.
Or do you mean that the library has these materials, but your people aren't in them under any spelling variant? I see they do have tax lists, deeds (partly indexed), and at least one county directory -- any hope there? They also have many years of chancery court files, which apparently are indexed volume by volume. (I haven't used these, but in Indiana those indexes are usually only by plaintiff, but at least you can read them faster than the full record.) I guess the next thing after that is to go after the families they married into and did business with, and try to come at them sideways. Hope this helps -- Harold
I'm guessing you've looked through Michigan GenWeb's site, already? Here's a link to Muskegon's listings just in case: http://www.usgwtombstones.org/michigan/muskegon.htm. Otherwise, I'm afraid the best I can offer is my sympathy. A number of my relatives seem to have vanished into thin air. Currently, I'm stuck on one of my grandfather's cousins, born in Michigan. He just disppears after about 1900.