[Plugin: Easy Add Thumbnail] The plugin cant grab from external source

Please, read the description of the plugin before creating a support thread…

There’s no “problem” here, read from first paragraph of plugin description:

Checks if you defined the post thumbnail, and if not it sets the thumbnail to the first uploaded image for that post. So easy like that…

So it’s normal to not work with external sources of images. Because the plugin (and WordPress) needs the image to be uploaded/attached to the post.