I have implemented same in one of my project requirement using functions “wp_get_post_tags” and “get_posts” to get related posts of same tags to which current post belongs to.
<?php
// Get tags of current post
$tag_objs = wp_get_post_tags($post->ID);
$tags = array();
foreach ($tag_objs as $tag_obj) {
$tags[] = $tag_obj->term_id;
}
// Get Posts
$myposts = get_posts(array(
'numberposts' => 6,
'tax_query' => array(
array(
'taxonomy' => 'post_tag',
'field' => 'term_id',
'terms' => $tags,
),
),
'post_status'=>'publish',
));?>
Hope this helps..!!