problem with fetching the most viewd posts/pages

Hi
I want to create a plugin that uses some filters to show posts and pages. For orderby filter, one of the options is ‘meta_value_num’ to get most views for posts or pages. To do this, if orderby value is ‘meta_value_num’ then meta_key value is set on ‘post_views_count’. But when I test my code, it returns nothing.(of course, with get_pages function some pages are returned, but for get_posts function nothing) I don’t know what is the problem. I searched for the answer in different websites, but I did not find a different way for showing most viewed posts. Please guide me. I test my code with wordpress 4.4.2.