Custom theme won’t use search.php

Why you are using this filter code, WordPress will still use searchform.php code, without it?

Further, it could be some issue with the loop code within search.php. Twentyfourteen theme looks for content-[post-format].php file. Do you have one in you theme root?

get_template_part( ‘content’, get_post_format() );

try using this simplified loop in search.php …

        <?php if(have_posts()) : while(have_posts()) : the_post(); ?>

            <?php the_content(); ?>

        <?php endwhile; endif; ?>