social bookmarking relies on opening accounts with the platforms , so you would need a twitter account , facebook , reddit , digg , blinklist , there are hundreds of them , i dont use more than twitter , facebook , digg and google+ at the minute , you can use a dashboard type app to make it easier and submit links remotely , the most well known being hootsuite although im unssure wether its a paid application now , i'll have to go and look

, ive not come across a paid service where others would do this for you so far, you still have to do it yourself albeit remotely from an app , i'lll have a mooch around and see wht i can find , personally the accounts i dont handle on a daily basis myself i run stright from my blogs using rss feeds , if you use wordpress its possible to schedule posts ...
I wouldnt mind doing it for you if you could provide details on what markets you want to hit and we could chat about the ins and outs of what where when and how ...
it's really a matter of choice as to how involved you wish to get on the various platforms , i like nattering to people so i find it quite easy to interact across facebook and the like , if you are thinking of using facebook then my opinion is that its necessary to get involved to a degree even if its just to initially get the page out there and gaining a following ..
as i said i'll have a mooch about and see what i can find that might help you out
Rainee x