How do you search for other users on the "overflow" sites?
Search for other users, eh? Given the date, I assume you mean, "...for romantic purposes". Nudge nudge, wink wink...
It's ok, you can admit it - everyone needs love sooner or later. However, I must caution you: angling for amour on SOFU is a game fraught with danger; sure, these sites might appear to be one big meat-market, stacked to the rafters with the lonely and the desperate... and sure, some of the bio photographs are down-right tantalizing... but all is not as it seems.
Uncle Shog's Quick Tips for Avoiding Mating Mishap on SOFU
Your question is a bit vague. You can search user questions by preceding your typical searches with:
Where the latter number is the userid. For instance, you could find all "greasemonkey" posts by myself by searching:
If you wanted to look up users by their display name (in whole or in part), you can do so by searching the Users tab at http://meta.stackoverflow.com/users - just begin typing in a name, and let the magical ajax take care of the rest.