Good question - digital B2B is definitely a particular challenge.
One factor that determines the approach is the nature of your potential buyers' online habits.
For example, if a significant percentage of your potential buyers use X social network, it makes sense to develop strategic marketing on X social network.
This means the first step in the process is defining your digital target market. You may have a good idea what your target market is offline, but you've got to hop inside their heads when they get online, either on a desktop or mobile.
It's true that there are myriad other ways to find your target market online beyond social media, but the value of social media lies in how most users declare who they are (and what their buying habits are) on their social networks (bio keywords, friends, hashtags, and other content they interact with).
In order to define your target market online, I recommend three different strategies:
1. Manageflitter (manageflitter.com) and Followerwonk. These tools are for Twitter only, but that's ok because Twitter is amazing. ;) Using the "Bio keyword search" or "account search", type in words your potential buyers might use to describe themselves. (You can also narrow it by location, which sounds valuable to your South Africa specification).
For example, your buyers might place "CEO" or "Owner" in their bio. (I have no idea, just giving an example). You will be able to view, classify, and interact with all the accounts on Twitter who match your specifications.
2. The other tool that aids greatly in target market definition online is Facebook Graph Search. It is a newer function of Facebook.
Here's how you can take advantage of it:
a. Find a very popular Facebook Page of a competitor or industry partner (or your own Facebook Page, if it has 500+ Likes). Let's say the page is named "Industry Partner"
b. Type in the search bar: "Magazines people who like Industry Partner like" or "Websites people who like Industry Partner like" or even "Restaurants people who like Industry Partner like".
With a large enough data pool, Facebook Graph Search provides an incredible amount of marketing insight: where your potential buyers eat, what they read, what websites they visit.
Repeat this process on as many relevant pages as possible.
If you find 3 websites they tend to like (ones that keep popping up), consider advertising via Google Adsense on those sites. Reach out to the admins of the sites (you may be able to find them by searching the site name on Twitter via Manageflitter or Followerwonk) and see if they are open to advertising or partnership opportunities -- perhaps a guest blog about how YOU are singlehandedly revolutionizing the industry.
There are more ways to accomplish what you are looking for, but I hope these help. I guarantee they're highly valuable for how much time they take.
Let me know if you would like more information.