Did you know LinkedIn has groups? Everything from A to Z as far as topics go. And I should know - I use it to market piano lessons of all things.
But the real beauty of using LinkedIn groups for marketing is that you can post to as many groups as you want at the same time with one click using the LinkedIn plugin. It's available on any 'Share' button.
What I do is post my own press releases from PRlog to stimulate conversation. Does it work? I'm pretty much the number one contributor for many of the groups I've joined.
Will this get you noticed among influencers in your area of expertise? Absolutely. But you have to make it interesting enough so others will respond and contribute. I do this via press releases.
P.S. You can do this with articles too!