personally i think there is a fine line/balance between: encouraging people to post one way or another on social media about/from your website ... and conversely putting others off by having too many buttons, especially those that don't use them.

i'm hoping to be able to find a way of calculating if a user is already logged onto one/any of the social media sites and presenting those users only with share/tweet etc buttons.

is there an easy way of doing this? i've been looking around the web and not found anything that works... how would you start to develop such a system?