Post thumbnails are not showing

Question

Why is not appearing the thumbnail in my Wordpress post?
I added the add_theme_support( 'post-thumbnails' ); in functions.php but still not showing up, my code in cont

<?php // Styling Tip! 

// Want to wrap for example the post content in blog listings with a thin outline in Bootstrap style?
// Just add the class "panel" to the article tag here that starts below. 
// Simply replace post_class() with post_class('panel') and check your site!   
// Remember to do this for all content templates you want to have this, 
// for example content-single.php for the post single view. ?>

<!--<article id="post-<?php the_ID(); ?>" <?php post_class(); ?>>-->


<div class="col-md-6">
<div class="row">

    <!--retirado daqui-->

    <div class="post-content-wrap col-sm-12 col-md-10">
       <header class="page-header">
        <h1 class="entry-title"><a href="<?php the_permalink(); ?>" rel="bookmark"><?php the_title(); ?></a></h1>
        <!--<span class="entry-author">
            <?php _e('Posted by', 'ascent') ?>
            <span class="author vcard entry-author-link">
            <?php the_author_posts_link(); ?>
            </span>-->
        </span>
        </header>  <!--.entry-header -->

    <?php if ( is_search() || is_archive() ) : // Only display Excerpts for Search and Archive Pages ?>
        <div class="entry-summary">
        <?php the_excerpt(); ?>
        <!--<a class="read-more" href="<?php the_permalink(); ?>"><?php _e('Read More &rarr;', 'ascent'); ?></a>--!>
        </div><!-- .entry-summary -->

    <?php else : ?>

        <div class="entry-content">
        <?php $format = get_post_format($post->ID); ?>
        <?php if (has_post_thumbnail($post->ID)): ?>
            <?php 
            $image_id = get_post_thumbnail_id();
            $full_image_url = wp_get_attachment_url($image_id);
            ?>
            <?php if ( '' != get_the_post_thumbnail() ): ?>
            <figure>
                <a class="swipebox" href="<?php echo $full_image_url; ?>" title="<?php the_title(); ?>">
                <?php the_post_thumbnail('blog-page'); ?>
                </a>
            </figure>
            <?php endif; ?>
        <?php endif; ?>

        <?php the_excerpt(); ?>

        <?php
            wp_link_pages( array(
            'before' => '<div class="page-links">' . __( 'Pages:', 'ascent' ),
            'after'  => '</div>',
            ) );
        ?>
        <a class="read-more" href="<?php the_permalink(); ?>"><?php _e('Read More &rarr;', 'ascent'); ?></a>

        </div><!-- .entry-content -->
    <?php endif; ?>

       <footer class="footer-meta">
        <?php if ( 'post' == get_post_type() ) : // Hide category and tag text for pages on Search ?>

            <?php
            /* translators: used between list items, there is a space after the comma */
            $categories_list = get_the_category_list( __( ', ', 'ascent' ) );
            ?>
            <?php
            /* translators: used between list items, there is a space after the comma */
            $tags_list = get_the_tag_list( '', __( ', ', 'ascent' ) );
            ?>

            <?php if ( ($categories_list && ascent_categorized_blog()) || ($tags_list) ): ?>
            <div class="cat-tag-meta-wrap">
                <?php if ( $categories_list && ascent_categorized_blog() ) : ?>
                <!--<span class="cats-meta"><?php printf( __( '<i class="fa fa-folder"></i> %1$s', 'ascent' ), $categories_list ); ?></span>-->
                <?php endif; ?>
                <?php if ( $tags_list ) : ?>
                <!--<span class="tags-meta"><?php printf( __( '<i class="fa fa-tags"></i> %1$s', 'ascent' ), $tags_list ); ?></span>-->
                <?php endif; ?>
            </div>
            <?php endif; ?>
        <?php endif; ?>
        </footer> <!-- .entry-meta -->          
    </div><!--.post-content-wrap-->

    </div><!--.row-->

</div>
<!--</article> #post-## -->

Answer 1

You need to create the thumbnail "blog-page" in your php Function. If you don’t know how to do this, you can use one of those non-wordpress natives.

<?php the_post_thumbnail( 'thumbnail' );       // Thumbnail (default 150px x 150px max)
the_post_thumbnail( 'medium' );          // Medium resolution (default 300px x 300px max)
the_post_thumbnail( 'large' );           // Large resolution (default 640px x 640px max)
the_post_thumbnail( 'full' );  > 

For more information on Codex.

I hope I’ve helped.