Theme Options: If There is No Input, Don’t Display?

Check if get_option returns a value and if it is not blank, then output the links.
This should work for you:

<?php
if(get_option('to_facebook') && get_option('to_facebook') != '') {
     ?>
     <a href="https://wordpress.stackexchange.com/questions/34948/<?php echo get_option("to_facebook'); ?>"></a>
    <?php     
}   
if(get_option('to_google_plus') && get_option('to_google_plus') != '') {
    ?>
    <a href="https://wordpress.stackexchange.com/questions/34948/<?php echo get_option("to_google_plus'); ?>"></a>
    <?php
}
?>