1) You may be targeting the wrong personas either a) at the comment / message stage, or b) at your landing page. If you're sure that you're targeting the right, and the same personas at both stages, then there's something wrong with the layout of your landing page (i.e. the actual visual layout and options for actions). There's no other reason why people would be bouncing off.

2) The most important advice for increasing click-throughs from a lot of those social sites is to make sure you are posting a lot of useful / interesting stuff that is _not_ a targeted marketing pitch. That will a) get more people to passively be attracted to your service, and b) it will increase your credibility, and c) increase likeliness of being upvoted / shared (since you will be less of an annoying marketer, and more someone that posts useful content, that also happens to sometimes pitch their product if it could be useful to someone).

Those are the two most important points, but there are a bunch of more subtle ones. If you'd like to talk about social media marketing specifically with respect to your product let me know,

best of luck,

Lee