featherodd

tried a bunch of solutions and this seemed to do the trick:

added this to functions.php:

function get_post_thumbnail_url() {
	$thumbnail_id=get_the_post_thumbnail($post->ID, thumbnail);
	preg_match ('/src="(.*)" class/',$thumbnail_id,$link);
	echo $link[1];
}

and this to my header:

<?php if (is_home()) : ?>
	<meta property="og:type" content="blog" />
<?php else : ?>
	<meta property="og:type" content="article">
	<link rel="image_src" type="image/jpeg" href="<?php get_post_thumbnail_url() ?>" />
	<meta property="og:image" content="<?php get_post_thumbnail_url() ?>"/>
<?php endif; ?>