this is definitely related to jetpack.
i didn't realize plugins could modify the php of your theme
I found these at the top of my spun footer.php (not my child theme)
$spun_facebook = get_theme_mod( 'jetpack-facebook' );
$spun_twitter = get_theme_mod( 'jetpack-twitter' );
$spun_tumblr = get_theme_mod( 'jetpack-tumblr' );
so, i don't quite know how to get these mods working, although i could try to repurpose the "linkedin" mod for google plus ... i don't know how well it would work..... i'd need to look for linkedin all over all the php files i guess. sounds like it's probably a little above my current coding level, unless there's an easy couple of changes i could make.