Use tool and target similar articles that went viral and create a CTA image with a link back to your articles.

Two good examples with a effective call to action are Evernote and Netflix.
For evernote the green color of the main and secondary CTA buttons is the same green as the headline and the Evernote logo, all of which jump off the page.

Also, you’ll notice at netflix again that the red color of the primary and secondary CTAs here match Netflix’s logo color. Tools

More examples: