[@vmodha Member 14 years, 2 months ago]

Solved!

SELECT * FROM $wpdb->posts
LEFT JOIN $wpdb->postmeta ON($wpdb->posts.ID = $wpdb->postmeta.post_id)
LEFT JOIN $wpdb->term_relationships ON($wpdb->posts.ID = $wpdb->term_relationships.object_id)
WHERE $wpdb->posts.post_type = 'forum'
AND $wpdb->posts.post_status = 'publish'
AND $wpdb->postmeta.meta_key = '_bbp_topic_count'
ORDER BY $wpdb->postmeta.meta_value DESC
LIMIT 100
";

$forum_posts = $wpdb->get_results($querystr, OBJECT);


if ($forum_posts)
{
    global $post;

    foreach ($forum_posts as $post)
    {
        setup_postdata($post);
        bbp_forum_title();
        the_content();
    }