This is definitely one I've experienced in moving from a company of ~50 employees to well over 200 (not including our parent company).
The biggest breakdowns are where things fall in the gap between two (or even three) departments.

(via +Michael Poloni 's Twitter)

Great article on this, and the suggestions at the end overall are good ones.

At one of my recent jobs, I had counted the ways in which someone might communicate to me a task that needed to be done. It ended up being 9.  Because the company didn't put any effort into addressing the communications gap as they grew, teams started to naturally silo and picked their own communications methods.

Very few other people had to deal with all 9 methods, usually teams only had 2-3 ways in and out.

Definitely recommend focusing on on-boarding as well. I tend to time how quickly a dev can go from starting the job to compiling the project locally. One place I worked, this ended up taking two months due to all the business silos, access hurdles, and tribal knowledge. If this is ever beyond a week or two, it's probably a sign on-boarding needs a lot of work.