Even management guru's thrive for word of mouth publicity and at times, are not able to get it. So, even I suggest its the best way, but at the same time the big question you should ask is about its reach?
Also, on the other hand, the time required. I believe these are the limitations, why organizations prefer advertisements.
Also, due to the advancement in the technology, involvement of mass people, global outreach,the advertisements on virtual space are becoming a popular and an affordable source as well. But again the biggest mistake which people do is not choosing the right platform.
Telling those, who listen, is the answer, i.e. promoting on a virtual place where your target market is the solution.
So in my view you should go ahead with Advertisements, preferably on virtual space
The company BusinessVibes, I work for is also catering to similar issues.
Please reach out to me if i could be any help at firstname.lastname@example.org