I have thumbnail support added with the following in my functions.php

```
// Add Thumbnail Support
add_theme_support('post-thumbnails');
set_post_thumbnail_size( 140, 140, true );

```

And I create the custom post type with

```
// Create Custom Post Type for Work
add_action( 'init', 'create_post_type' );
function create_post_type() {
register_post_type( 'custom_post',
    array(
        'thumbnail',
        'labels' => array(
            'name' => __( 'Custom' ),
            'singular_name' => __( 'Custom' )
        ),
        'public' => true,
        'has_archive' => true,
        'rewrite' => array('slug' => 'custom'),
        'taxonomies' => array('category', 'post_tag')
    )
  );
}

```

However, when I create a new post in the Custom Post Type, the Featured Image meta box does not show. I have also tried using an array when declaring the custom post type, as follows but that didn't work either

```
// Add Thumbnail Support
add_theme_support('post-thumbnails', array ('post','work','custom_post'));
set_post_thumbnail_size( 140, 140, true );

```

What am I missing?