Font Awesome must be in use on the website for icons to show.

Jetpack Share CSS with Font Awesome

/*
Jetpack Sharing
---------------------------------------------------------------------------------------------------- */
 
div.sharedaddy div.sd-block {
	border: none;
	padding: 0;
}
 
div.sharedaddy .sd-content {
	float: left;
	margin-bottom: 32px;
}
 
div.sharedaddy a.sd-button {
	border: none !important;
	box-shadow: none;
}
 
.sd-social-icon-text a.sd-button > span, a.sd-button > span {
	opacity: 1;
	padding: 6px 12px;
}
 
a.sd-button > span {
	background-image: none !important;
	background: #1671f0;
	border: none;
	color: #fff;
	font-size: 12px;
	font-weight: 400;
	letter-spacing: 1px;
	text-transform: uppercase;
}
 
a.sd-button:hover > span {
	background: none;
	color: #333;
	}
 
.sd-content .sd-button span.share-count {
	color: #e5e5e5 !important;
	font-size: 100% !important;
}

li.share-facebook a.sd-button>span  {background: #3b5998;}
li.share-facebook a.sd-button>span:before {
	content: "\f09a";
	font-family: FontAwesome;
	padding-right: 4px;
	}
li.share-twitter a.sd-button>span  {background: #00aced;}
li.share-twitter a.sd-button>span:before {
	content: "\f099";
	font-family: FontAwesome;
	padding-right: 4px;
	}
li.share-google-plus-1 a.sd-button>span  {background: #dd4b39;}
li.share-google-plus-1 a.sd-button>span:before {
	content: "\f0d5";
	font-family: FontAwesome;
	padding-right: 4px;
	}
li.share-linkedin a.sd-button>span  {background: #007bb6;}
li.share-linkedin a.sd-button>span:before {
	content: "\f0e1";
	font-family: FontAwesome;
	padding-right: 4px;
	}
li.share-pinterest a.sd-button>span  {background: #cb2027;}
li.share-pinterest a.sd-button>span:before {
	content: "\f0d2";
	font-family: FontAwesome;
	padding-right: 4px;
	}
li.share-stumbleupon a.sd-button>span {background: #f74425;}
li.share-stumbleupon a.sd-button>span:before {
	content: "\f164";
	font-family: FontAwesome;
	padding-right: 4px;
	}
li.share-print a.sd-button>span:before {
	content: "\f02f";
	font-family: FontAwesome;
	padding-right: 4px;
	}
li.share-email a.sd-button>span:before {
	content: "\f0e0";
	font-family: FontAwesome;
	padding-right: 4px;
	}