Maybe this could be useful.
I used it on my own site to display a list of thumbnails.
<?php
// check if there's a thumbnail
if ( has_post_thumbnail($post->ID)) {
//show thumbnail
echo 'get_the_post_thumbnail($post->ID, 'thumbnail' , array('class' => "img-responsive yourClass"));
} else {
//show another image if there's not a thumb
echo '<img class="img-responsive" src="'.get_template_directory_uri().'/MISSING-PHOTOS.jpg">';
}
?>
Hope can help you.