News Slider default image

Hi so basically I noticed that if I add a post without a featured image, the post won’t show up in the news slider. This is im pretty sure the people using this site won’t always have a site. Is there a way I can set a featured image by default if they do not have a default image? or get my posts to show anyway? 
 
I tried using the Default featured Image plugin, but it still does not work! 
Thank’s and be