Pinterest is an image based site and requires an image to be set along with the PinIt button to be shared back to Pinterest. For Joomla content, K2 items and various other extensions, JFBConnect can automatically detect the image to be set. If no image can be found to be set, then JFBConnect will not show the Pinterest button, because it won't work.
With that said, please:
* Add an image to your article, either in the text or using the "Image" parameter
* Then, enable the Open Graph - Content plugin
Alternatively, to set a default image (like a logo) to use on all of your pages in case an image can't be found, please:
* Go to the JFBConnect -> Open Graph -> Settings area
* In the Defaults box, add a line like:
image=http://yoursite.com/link-to-logo.jpg
That will give you a good fallback to try and always show the Pinterest button on all content.
I hope that helps,
Alex