Home Page Thumbnail image not Showing

Hi Friends, I having a problem with image in my website. I have started my site 3 months ago. https://www.crazyboys.org . From the First day i am facing one problem. Whenever I am using a theme with thumbnail image with post in home page, the thumbnail of the image is not showing. But when I am clicking the post to view the complete post, everything is fine there. I have tried various themes but the problem is still the same for all the themes. Please Help me out of this.