Use placeholder to prevent using the find box to add new members.

app/views/groups/members.html.haml

@@ -12,7 +12,7 @@
 .clearfix.js-toggle-container
   = form_tag members_group_path(@group), method: :get, class: 'form-inline member-search-form'  do
     .form-group
-      = search_field_tag :search, params[:search], { placeholder: 'Find member by name', class: 'form-control search-text-input input-mn-300' }
+      = search_field_tag :search, params[:search], { placeholder: 'Find existing member by name', class: 'form-control search-text-input input-mn-300' }
     = submit_tag 'Search', class: 'btn'
   - if current_user && current_user.can?(:manage_group, @group)