A search module is planned in a future release, but that won't be any time soon. I'm also working on a Joomla Smart Search indexer plugin that'll be available not longer after CB Activity 6.0.0 stable release so probably won't be until sometime in January.
However userlists allow external GET/POST unless you've hotlink protection toggled on in the userlist. This means you can just make your own form to search the userlist. Example as follows.
Code:
<form action="USERLIST_URL_HERE" method="post">
<input type="hidden" name="listid" value="USERLIST_ID_HERE">
<input type="text" name="name" value="" />
<button type="submit">Search</button>
</form>
Replace USERLIST_URL_HERE with the URL of your userlist. Replace USERLIST_ID_HERE with the id of your userlist. in the above example it will search the Name field. You can for the most part copy and paste the form HTML from a userlist itself and it will just work. Recommend using a CB Content Module or Joomla Custom HTML module for this.