facebook thumbnails missing

To instruct facebook which image to use as thumbnail on the wall, it is suggested to include special Open Graph meta tags within the head tag. For the thumbail image this is:

<meta property="og:image" content="path/to/image.jpg"/>

Put your logo somewhere on your server and point to it with an absolute path. If the image has the correct size (bigger than 50x50 px), file type (jpg, png or gif) and aspect ratio (max.3:1), latest after 24h you should see the logo aside your url when writing a new message in facebook and providing the link.

You also can force facebook to clear it's cache and analyze your website immediately. To do so, you have to enter your url in the so called Linter