I recently updated the Facebook Meta Tags plugin to use site logo if no thumbnail exists. To enable this feature you will need a simple edit in your functions file. Here is how to do this.
Facebook Meta Tags plugin automatically adds required meta tags for the facebook share. It uses post title, generates a short excerpt from post content and uses post’s Featured Image as share thumbnail. However if no thumbnail exists, it needs some more information to be set.
To provide this additional data you need to put the following line in your
functions.php file in your theme folder.
update_option('logo_url', 'https://wpassist.me/wp-content/themes/construction/images/shailan_logo.png'); // <- Put your logo url instead of mine
This simple option will set up a default thumbnail for the plugin.