a4est42: I only got my AncestryDNA results yesterday so haven't had much time with the match list, but yes I intend to pursue it. I misspoke when I said the closest match was 4th cousin. There are about half a dozen 3rd-4th cousins. I went through all of their trees (if they had a public one) and wrote every one, saying if I thought the potential for a match was in a particular direction. Of the private trees, one gave me access and the other wrote back after looking at my tree.
Another one had a surname match that didn't come up on Ancestry's little surname box, because of the spelling variation. I'm a Deutelbaum and am pretty sure at this point that *all* Deutelbaums from Hungary/Slovakia are related to me. This match had some Teutelbaums, which is a common variant but said they were from "Russia." Russia is a huge catchment for American Jews from Eastern Europe, but I've never seen it applied to anything but the most eastern reaches of the Hungarian Empire (certainly not NW Slovakia).
I also looked at the profiles of a couple dozen other matches, chosen somewhat randomly (but looked for larger public trees). Looked at surnames and locations and at their trees. Nothing.
I realize I only have solid lines for 2nd cousins (I know all my great grandparents with a good amount of detail) and a few up to 3rd cousins (great great grandparents). But in 3 large DNA matching sites I have yet to find a common surname (that isn't super common and from the wrong area) or town (other than big ones). Sure, I could be fairly closely related to someone who doesn't know their great grandma's maiden name so the connection isn't visible. But you think there'd be one common surname or knowing we were from the same small region in Europe where everyone was cousins (if you're a Jew with ancestry in Kotesova, Slovakia, I guarantee we're related).
It's a bit frustrating and disappointing, but I am far from giving up. And I've had enough positives from the testing to make it worthwhile. I figure if I can find just one match on each line, it will open up the floodgates for others, because I'll be able to expand my tree (provisionally if there aren't source materials, but still enough to get clues to go further).