app/views/reports/_search.html.erb
<%= form_tag url_for(controller: 'reports', action: 'custom_search', id: @report.id), remote: true, class: 'form-horizontal' do %>
<div class="input-group">
<%= search_field_tag 'search', nil, class: 'form-control' %>
<span class="input-group-btn">
<%= submit_tag 'Search', class: 'btn btn-default', title: 'Search' %>
</span>
</div>
<% end %>