You are welcome Anand. As I'd shared earlier, you should segment your target audience in terms of various parameters. Based on that identify the channels (e.g. Facebook, LinkedIn, Twitter, Google etc) on which your audience is present followed by reaching out to them to initiate conversation with them leading to ultimate customer acquisition.
E.g., by following steps mentioned through the below link, even without starting your ad, you can validate if your target audience is on Facebook.
You can do the same on LinkedIn Ads interface. On Google, you can find out the number of searches for a keyword in a selected region through Google Keywords Planner tool, which is part of Google AdWords:
On a different note, we've just published an article on Digital Marketing for Healthcare.