Change order to Random for related posts list

I have created a bit of code that is hooked beneath each post. It displays the thumbnail and title of 4 posts from the same category as the preceding post.

It works perfectly, the only thing I want to change is to have it choose the 4 posts from the category RANDOMLY. Currently it seems to be pulling th 4 most recent posts.

How do I change my code to facilitate this?

function my_related_posts() {
if (is_single()) {
	global $post;
	$current_post = $post->ID;
	$categories = get_the_category();
foreach ($categories as $category) :
	?>
<div class="featured-posts-box"><div class="my-recent-posts"><h4>You may also like...</h4><ul class="top-featured-image">
	<?php
	$posts = get_posts('numberposts=4&category='. $category->term_id . '&exclude=' . $current_post);
foreach($posts as $post) :
	?>
<li  class="top-featured-image"><span><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></span> <?php if ( has_post_thumbnail()) : the_post_thumbnail('thumbnail'); endif; ?></li>
	<?php endforeach; ?><?php endforeach; ?>
</ul>
</div>
</div>
	<?php
		}
	wp_reset_query();
}