buttons not rendering

I have a node type that use a tpl.php template to render the fields.
The template doesn't contain a:
print render($content);

I have tried to add:
print render($content['sharethis_field']);
but it doesn't show anything.

If I set "Links area " in the location options than the buttons show properly at the botton of the page (not rendering is required since I have a print render($content['links']); instruction).

Any idea on how to show the buttons without rendering the whole content?