Show empty categories within Woocommerce. Paste this in to your theme's functions file. It's just a copy and paste of a function within woocommerce-template.php and changing value of hide_empty to 0

Woocommerce - show empty categories

// Paste this in to your theme's functions file
// Redefine sub category display to output empty categories
function woocommerce_product_subcategories( $args = array() ) {
	global $woocommerce, $wp_query, $_chosen_attributes;

	$defaults = array(
		'before'  => '',
		'after'  => '',
		'force_display' => false
	);

	$args = wp_parse_args( $args, $defaults );

	extract( $args );

	// Main query only
	if ( ! is_main_query() && ! $force_display ) return;

	// Don't show when filtering
	if ( sizeof( $_chosen_attributes ) > 0 || ( isset( $_GET['max_price'] ) && isset( $_GET['min_price'] ) ) ) return;

	// Don't show when searching or when on page > 1 and ensure we're on a product archive
	if ( is_search() || is_paged() || ( ! is_product_category() && ! is_shop() ) ) return;

	// Check cateogries are enabled
	if ( is_product_category() && get_option( 'woocommerce_show_subcategories' ) == 'no' ) return;
	if ( is_shop() && get_option( 'woocommerce_shop_show_subcategories' ) == 'no' ) return;

	// Find the category + category parent, if applicable
	if ( $product_cat_slug = get_query_var( 'product_cat' ) ) {
		$product_cat = get_term_by( 'slug', $product_cat_slug, 'product_cat' );
		$product_category_parent = $product_cat->term_id;
	} else {
		$product_category_parent = 0;
	}

	// NOTE: using child_of instead of parent - this is not ideal but due to a WP bug ( http://core.trac.wordpress.org/ticket/15626 ) pad_counts won't work
	$args = array(
		'child_of'		=> $product_category_parent,
		'menu_order'	=> 'ASC',
		'hide_empty'	=> 0,
		'hierarchical'	=> 1,
		'taxonomy'		=> 'product_cat',
		'pad_counts'	=> 1
	);
	$product_categories = get_categories( $args  );

	$product_category_found = false;

	if ( $product_categories ) {

		foreach ( $product_categories as $category ) {

			if ( $category->parent != $product_category_parent )
				continue;

			if ( ! $product_category_found ) {
				// We found a category
				$product_category_found = true;
				echo $before;
			}

			woocommerce_get_template( 'content-product_cat.php', array(
				'category' => $category
			) );

		}

	}

	// If we are hiding products disable the loop and pagination
	if ( $product_category_found == true && get_option( 'woocommerce_hide_products_when_showing_subcategories' ) == 'yes' ) {
		$wp_query->post_count = 0;
		$wp_query->max_num_pages = 0;
	}

	if ( $product_category_found ) {
		echo $after;
		return true;
	}

}

Great, just what I needed! Do you also have a solution for the product categories widget to show empty categories? Cheers!

Wow, thank you so much! I notice that this addition makes products show up on the shop page, even though my settings are correct to make them not show up. I have tried editing this addition, but I can't get the products to go away. Would it be possible for you to help me edit this to prevent products from appearing on the shop page? I would really appreciate it! The shop is http://www.pacsglobal.com/shop which only has 2 categories and 1 item until I can get this issue handled.

// WooCommerce Code
add_filter('woocommerce_product_subcategories_args', 'woocommerce_show_empty_categories');
function woocommerce_show_empty_categories($cat_args){
$cat_args['hide_empty']=0;
return $cat_args;
}

In your functions.php is all you need... not all of this.

All of that big chunk of function works for me, and filter doesn't... :-( Guess I'll stay with large chunk.

Better yet, since version 2.2.6 released on 08/10/2014:

add_filter('woocommerce_product_subcategories_hide_empty', 'woocommerce_show_empty_categories', 10, 1);

function woocommerce_show_empty_categories($show_empty){
    return true;
}

@dalemoore's solution would have worked on old versions of WooCommerce, but at some point they switched over to this new woocommerce_product_subcategories_hide_empty filter, which occurs after the categories are retrieved with the arguments provided by the woocommerce_product_subcategories_args filter.

You can actually use predefined core function __return_true(), so the whole thing transforms into one line of code in your functions.php:

add_filter( 'woocommerce_product_subcategories_hide_empty', '__return_true');

StingerDevlab.
Yup that's the fix, nice & simple
Still works as of this post with WP 4.6 & WooCommerce 2.6.4
I just wish they would put a 'show empty categories' button, enough people are calling for it to warrant it's inclusion

Works for me better and more simple:
Code for WooCommerce 3.x+

function hide_empty_categories ( $hide_empty ) {
    $hide_empty  =  FALSE;
    // You can add other logic here too
    return $hide_empty;
}
add_filter( 'woocommerce_product_subcategories_hide_empty', 'hide_empty_categories', 10, 1 );

Pre 3.x Code

function show_empty_categories ( $show_empty ) {
    $show_empty  =  TRUE;
    // You can add other logic here too
    return $show_empty;
}
add_filter( 'woocommerce_product_subcategories_hide_empty', 'show_empty_categories', 10, 1 );

aliomaster, thanks a lot!

almazka987 Thanks. That worked like a charm