How to add StumbleUpon (and others) to your Blog Share Buttons…
I always recommend that WordPress Bloggers (especially Authors) activate ‘Publicize’ so their posts are automatically uploaded to their media pages (but they will need to have accounts there)
ALSO, add every available share button that WP offer.
These buttons can then be used by their visitors, regardless of whether or not the posting bloggers themselves have accounts in the various media.
This enables visitors, like me, to share and spread their posts further – for Authors especially, this increases their marketing range A LOT.
One button that is not offered by WP is StumbleUpon, but you can add your own (and possibly others), by following this Step-by-Step guideline article by Michael A Rios
Click on the link or his photo below: