Yes, the instagram icon is missing . Instagram was not active when this theme was released.
You need to change the code to add a new social icon.
To add a new social icon in the social shortcode –
First modify the image images/social-icons/social.png and replace the original file in the images folder with the new one.Then you need to modify the file framework/shortcodes/social-shortcodes.php
To add a new social icon in the social network-widget-
1.Modify the image images/social-icons/social-widget.png and images/social-icons/social-widget-hover.png and replace the original file in the images folder with the new one.
2.Pls modify file framework/widgets/mo-social-networks-widget.php.
Hope this helps.