Note: This article applies for the themes that include a sociable icons set in the header or footer of the theme.
How can I add a custom icon to the default sociable icons set?
First, if you don’t have the icon image, you can refer to the “PhotoShop files and image resources” section of the documentation to find the website where the icons used in the theme are downloaded from. After you open the icons download page, you can look for the icon image you would like to add. If the icon pack doesn’t include the image, you can do a quick Google search to find an icon that would match the currently included icons.
After you have the icon image, the easiest way to add it would be to replace one of the existing icon images that you are not going to use with your new icon image. The icons are located within the images/icons folder of the theme. If, however, you prefer not to replace the icon, but add it as a new icon, you would have to add its file name to the $sociable_icons array which should be located in the beginning of the lib/options/general.php file of the theme.