A function that curates share-permalinks to Facebook, Twitter, Reddit, Tumblr, Google+, Pinterest, Stumbleupon, etc. The function generates the URL for you.

get_share_link.php

<?php

function get_share_link($url, $image, $title, $description, $network) {
    $networks = [
        'twitter' => function($url, $title) {
            return 'https://twitter.com/intent/tweet?text=' . urlencode($title . ' ' . $url . '?network=twitter');
        },
        'facebook' => function($url, $title, $image, $description) {
            return 'http://www.facebook.com/sharer.php?s=100' . 
                '&p[url]=' . urlencode($url . '?network=facebook') .
                '&p[title]=' . urlencode($title) . 
                '&p[images][0]=' . urlencode($image) . 
                '&p[summary]=' . urlencode($description);
        },
        'reddit' => function($url, $title) {
            return 'http://www.reddit.com/submit?title=' . urlencode($title) . '&url=' . urlencode($url . '?network=reddit');
        },
        'google' => function($url) {
            return 'https://plus.google.com/share?url=' . urlencode($url . '?network=google');
        },
        'link' => function($url) {
            return $url . '&network=link';
        },
        'pinterest' => function($url, $image, $title) {
            return 'http://pinterest.com/pin/create/button/?url=' . urlencode($url  . '?network=pinterest') . '&media=' . urlencode($image) . '&description=' . urlencode($title);
        },
        'stumbleupon' => function($url, $title) {
            return 'http://www.stumbleupon.com/submit?url=' . urlencode($url  . '?network=stumble') . '?title=' . urlencode($title);
        },
        'tumblr' => function($url, $description) {
            return 'http://www.tumblr.com/share/link?url=' . urlencode($url  . '?network=tumblr') . '&description=' . urlencode($description);
        }
    ];

    if (isset($networks[$network])) {
        return $networks[$network]($url, $title, $image, $description);
    } else {
        return $url . '&network=link';
    }
}

// Example usage:
$url = get_the_permalink();
$image = wp_get_attachment_image_src(get_post_thumbnail_id(), 'thumb' );
$description = get_the_excerpt();
$title = get_the_title();

echo get_share_link($url, $image, $title, $description, 'facebook');
echo get_share_link($url, $image, $title, $description, 'twitter');
echo get_share_link($url, $image, $title, $description, 'reddit');