Featured image metabox not showing up

I have a theme installed on WordPress Multisite 3.5.1 which has a one custom post. Now I wanted to have two more so I have created them. Everything is working besides one thing. The featured image metabox is not showing up. I have added it to custom post

   $args = array(
        'labels' => $labels,
        'public' => true,
        'exclude_from_search' => false,
        'publicly_queryable' => true,
        'show_ui' => true,
        'rewrite' => array( 'slug' => $md_cssitems_rewrite ),
        'menu_icon' =>  get_template_directory_uri() . '/admin/assets/images/icon-porfolio-16x16.png' ,
        'query_var' => true,
        'capability_type' => 'post',
        'hierarchical' => false,
        'menu_position' => 8,
        //features support in Pofolio post type  
        'supports' => array('title','editor','excerpt','thumbnail','page-attributes')
      ); 

I also have read I might need to activate it using in my functions.php

add_theme_support( 'post-thumbnails',array('custom-post1','custom-post2') );

I also have checked in screen options and it is not hidden there.

I am running out of ideas. What else might be wrong?