Hi,
It is not a plugin or component that we used in our VM Template for those buttons.
We just browsed
www.addthis.com, chose the style for buttons, generated the CODE and pasted them to our VM Template's product details PHP file.
You can try sharethis.com though, basically they work the same.
The PHP file you need make edit is this:
ROOT/templates/<yourjoomlatemplate>/html/com_virtuemart/productdetails/default.php
and look for "addthis" in this file, you will find the HTML code that was generated from addthis.com, just replace them with the new one you just generate from sharethis.com.
OR, you can manually generate those buttons from FACEBOOK's and TWITTER's developer pages. (google them).
Cheers.