I dont know if this is what you want to do but let's see. I needed to add to social shares of those at end of article (two spanish social pages). So in /components/com_k2/templates/default/item.php there's a line "itemSocialLinksBlock" that is a list <li> All you have to do is add the new line like i did:
<li><a class="tuenti" title="<?php echo JText::_("Añadir a Tuenti"); ?>" href="
www.tuenti.com/share?url=<?php echo $this->item->socialLink; ?>&t=<?php echo urlencode($this->item->title); ?>" target="_blank"><span><?php echo JText::_("Añadir a tuenti"); ?></span></a></li>
You must konw how is the link to add shares in linkedin in tuenti it is "
www.tuenti.com/share?url=........"
