The below topic explains how to search a userlist with a custom form.
www.joomlapolis.com/forum/professional-members-support/246374-search-module?start=6#336251
Below is a working example using our demo site.
Code:
<form action="/community/members" method="post">
<input type="hidden" name="listid" value="4">
<input type="text" name="name" value="" />
<button type="submit">Search</button>
</form>
With this example it will search the userlist for the name field. You can use whatever form you like to do this as long as the URL points to the userlist, is a POST, and supplies the listid. The only requirements beyond that are you can only search fields that are searchable on that userlist. This is just a basic standard HTML form there's nothing further needed.