ok this is what i did.. 

in ow_plugins/sharethissocial/init.php

find this:

function sharethis_sharetool()
{

add after: 

//added to prevent sharethis display when not logged in
if (!empty($_COOKIE['ow_login']) && OW::getUser()->isAuthenticated() )
{

find this:

}

$display = "<div style=\"position:fixed; left:0px; bottom:3px;\">
<script type=\"text/javascript\">var switchTo5x=true;</script>
<script type=\"text/javascript\" src=\"http://w.sharethis.com/button/buttons.js\">
</script><script type=\"text/javascript\">stLight.options({publisher: \"\"});</script>
$sharetool</div>";

add after:

}else{
      // if not logged in then do not display
      $display = "<div style=\"display:none;\"></div>";
       }//close else