A class file that outputs social sharing buttons for WordPress, instantiated by array

class.social-share.php

<?php

/**
 * Class social_share
 * @author : Ian Armstrong (@imperativeideas)
 * A class file that outputs social sharing buttons for WordPress, instantiated by array
 */

/* Sample Usage:

$socialshares = new social_share(array(
    'facebook' => '',
    'linkedin' => '',
    'google' => '',
    'twitter' => array(
        'text' => get_the_title(),
        'hashtags' => naked_cats(), // function outputs cats without links
    ),
    'pinterest' => array(
        'media'         => wp_get_attachment_url( get_post_thumbnail_id($post->ID) ),
        'description'   => strip_tags(strip_shortcodes(get_the_excerpt())),
    ),
));

echo $socialshares;

*/

class social_share {
    protected $url;
    protected $networks = array();
    public  $shareset = array();

    /**
     * Constructor
     * @param array $networks :: networks for sharing are supplied by each page on instantiation
     */
    function __construct($networks = array()) {
        global $post;
        $this->url = get_the_permalink($post->ID);

        // Ensure that this is actually an array
        if (!array($networks)) {
            trigger_error('Unable to construct social output in ' . get_class($this) . 'using the given input');
        }

        // If there is at least one value, populate
        if (count($networks) > 0) {
            foreach ($networks as $name => $meta) {
                $this->networks[] = $name;
                $this->shareset[$name] = $this->make_share_link($name, $this->url, $meta);
            }
        }
    }

    /**
     * Outputs formatted links that target social sites with the shared content request
     * @param $network
     * @param $url
     * @param bool $meta
     * @return null|string
     */
    private function make_share_link($network, $url, &$meta=false) {
        $share_link = NULL;
        switch($network) {

            // Facebook is nice and easy
            case 'facebook' :
                $share_link = "https://www.facebook.com/sharer.php?u=" . $url;
                break;

            // LinkedIn also keeps things on the smooth tip
            case 'linkedin' :
                $share_link = "https://www.linkedin.com/shareArticle?mini=true&url=" . $url;
                break;

            // Google comes in with a "me too"
            case 'google' :
                $share_link = "https://plus.google.com/share?url=". $url;
                break;

            // Twitter is more complex with its hash tag array, based on post categories (if available)
            case 'twitter' :
                $tweet = "";
                $hashtags = "";
                if(array_key_exists('hashtags', $meta)) {
                    $count = count($meta['hashtags']);
                    $i = 0;
                    foreach( $meta['hashtags'] as $key => $value ) {
                        $hashtags .= htmlspecialchars($value);
                        $i++;
                        if ( $i != $count ) {
                            $hashtags .= ",";
                        }
                    }
                }
                if(!empty($meta['text'])) {
                    $tweet = htmlspecialchars($meta['text']);
                }
                $share_link = "http://twitter.com/share?url=" . $url;
                    if(!empty($tweet)) : $share_link .= "&text=" . $tweet; endif;
                    if(!empty($hashtags)) : $share_link .= "&hashtags=" . $hashtags; endif;
                break;

            // Pinterest - ignore the API docs, it's easier than all that noise
            case 'pinterest' :
                if(empty($meta['media'])) {
                    $share_link = NULL;
                } else {
                    $media = $meta['media'];
                }
                if(!empty($meta['description'])) {
                    $description = htmlspecialchars($meta['description']);
                }
                $share_link = "http://pinterest.com/pin/create/link/?url=" . urlencode($url);
                if(!empty($media)) : $share_link .= "&media=" . urlencode($media); endif;
                if(!empty($description)) : $share_link .= "&description=" . urlencode($description); endif;
                break;
            default :
                $share_link = NULL;
        }
        return $share_link;
    }



    /**
     * Allow the class name to be echoed directly without calling the display method
     * @return string
     */
    function __toString() {
        return $this->display();
    }

    /**
     * Display the class result as HTML
     * @return string
     */
    public function display() {
        $output  = "<div class='output-social'><ul>";

        foreach( $this->shareset as $name => $link ) {
            if( !empty($link)) :
                $output .= "<li class='{$name}'>";
                $output .= "<i class='icon-{$name}'></i>";
                $output .= "<a href='{$link}' target='_blank'></a>";
            endif;
        }
        $output .= "</ul></div>";
        return $output;
    }
}

/**
 * Get a simple array of assigned categories without links
 * @return array
 * Used by: class.social-share.inc
 */
function naked_cats() {
    global $post;
    $thecats = get_the_category($post->ID);
    $term_list = array();
    foreach ($thecats as $term) {
        foreach ($term as $key => $named_cat) {
            if('cat_name' == $key ) {
                $term_list[] = $named_cat;
            }
        }
    }
    return $term_list;
}

You can find some additional share strings here, if you want to expand this for Reddit, Digg, etc
https://simplesharebuttons.com/html-share-buttons/