By default there is a Facebook Recommend and a Twitter Share widget that appears on the front-end of your Appstore. You can manually change the Fan Page and Twitter handle affiliated with these properties by going to your Appstore Settings > General - Social Settings menu.
Inside these settings you will find a text property called 'Facebook Like Button URL' and 'Twitter Handler'.
For Facebook, paste the exact URL for your Facebook Fan Page.
For Twitter, post your exact Twitter hande without the @.