@Sevian: Oh so you want to add Featured Image in your Search result posts. This is quite technical task.
1. First you need to build child theme
2. Then copy content-single.php in your child theme and find the following code in this file
if ( is_search() ) : // Only display Excerpts for Search ?>
<div class="entry-summary">
<?php the_excerpt(); ?>
</div><!-- .entry-summary -->
3. then replace the above code with the following:
if ( is_search() ) : ?>
<div class="entry-summary">
<?php if( has_post_thumbnail() ):?>
<a href="<?php the_permalink(); ?>" title="<?php printf( esc_attr__( 'Permalink to %s', 'catchevolution' ), the_title_attribute( 'echo=0' ) ); ?>" rel="bookmark">
<?php the_post_thumbnail( $imagesize ); ?>
</a>
<?php endif; ?>
<?php the_excerpt(); ?>
</div><!-- .entry-summary -->
.
