This snippet allows you to convert a WordPress tag into a hashtag that links to a tag.
It works by scanning the content for the octothorp symbol (#) and changing the word right after the # symbol to a tag-link.

Add this snippet to the functions.php file of your active theme.

function wptag_to_hashtag($mywp_post)
	$content = $mywp_post->post_content;
	$ID = $mywp_post->ID;
	preg_match_all('/\B(\#[a-zA-Z]+\b)/', $content, $matches, PREG_PATTERN_ORDER);
	if (isset($matches[1])) {
		foreach ($matches[1] as $matchKey) {
			wp_set_post_tags($ID, $matchKey, true);
add_action('post_save', 'wptag_to_hashtag', 10, 2);
function hashtagger($content)
	$siteurl = get_site_url(); // get wordpress siteurl to create url for tags
	$content = preg_replace('/([^a-zA-Z-_&])#([a-zA-Z_]+)/', "$1<a class=\"hashtags\"  href=\"$siteurl/tag/$2\" target=\"_parent\" >#$2</a>", $content);
	return $content;
add_filter('the_content', 'hashtagger');