Hi,
Just activating the plugin should be enough.
There are several possible issues:
- the access setting of the plugin is not public
- there is some caching on your website
- your template has customized the product page and removed the social networks display.
So check the settings of the plugins, that you don't have caching activated, and if that doesn't help, try to switch your Joomla template to the default one. If it comes from the template, you can rename the files beginning with "show" in the folder templates/YOUR_TEMPLATE/html/com_hikashop/product/ via FTP and that should fix the problem