I'd go through an inicial test phase using programmatic media buying to identify a few insights first. With that, I would probably target the most efficient channels and set up an inbound strategy to capture​ leads. I would also try Google AdWords, but I can see that being costly. Facebook interest targeting would be something to try, especially if there are user groups related to the specific medical conditions you need to target. To get to a more specific strategy or tactics, I would need to have more concrete information... Hope that helps!

Francisco has a good answer. I especially agree w/ the Inbound strategy.

Put yourself in their shoes and predict what they're thinking/wondering/asking about. Create a content publishing strategy around those topics/questions.

The forums you mention will be a goldmine. Read the discussions and look for patterns in the language these patients use. Make sure your publishing matches their language.

Look for patterns in the patient profile, too.

Are they all likely to be 65+? Likely to be overweight? Likely to be male? Likely to be white/caucasian? Etc etc. If you can identify a persona, it will make ad targeting easier.

For example, 80% of mesothelioma patients are male. 95% are white. Knowing that, you could safely advertise to white men with a degree of confidence in your targeting.

The last strategy you may want to consider is a social media-focused 'shareable' campaign. Write/create/produce some piece of content about your cause with a strong TAKE OUR SURVEY call-to-action. (A poignant, touching, emotional video comes to mind, but I suppose it depends on the condition in question.)

The further the video spreads online, the more exposure your survey receives.

There are survey research firms with consumer panels that target medical conditions. There are many such companies, and I'd suggest reaching out to several to get competitive bids -- both on price and quality of respondents. You might even want to ask them to launch a test survey to understand the incidence rate in their panel, even after they deploy to a targeted group of panelists. It will be expensive, though.

I've had good experiences working with Survey Sampling (SSI) and Harris Interactive in the past. There are dozens if not hundreds of others. Some are listed here: https://www.greenbook.org/market-research-firms/online-surveys

I'd be happy to talk about the process - or create an RFP to send to research firms and evaluate the responses.

Good luck!

Try Traffic Oxygen as this tool allows creating custom audiences for many networks, not just Facebook.

This may be what you're after.

And, you can always start with Facebook... which is cheap + fast to run initial testing.

I like TJ's answer. An alternative strategy: Get to know some doctors who treat the patients of interest. Tell them you're doing some research for your product or service. If they seem interested, ask if they would be willing to hand out a form for you during appointments for those patients.

Make sure you have a good idea of what you want the doctors to tell the patients, including that the form is optional, that it's from an external research team, and how it will help the patient if you had the information (you'll be able to use it to improve certain aspects of their condition).

Most people are used to filling out forms at the doctor's office, and as long as you keep it anonymous you won't break confidentiality laws. Just come and collect the forms that have been completed at the end of the week.

I'd be happy to discuss what to do after the results come in.

In addition to the previous answers, the connecting with outspoken advocates for the health condition you're targeting. Leverage their platform for an authentic connection.

The web site Patients Like Me is a great place for you to gain access to a network with the specific conditions you are looking for. Also, you might want to try various professional societies to tap into the network of providers treating the individuals with the specific health conditions. For instance, if you are looking for people with heart disease, look at the American College of Cardiology and see what they offer for patient support in terms of networks, blogs, etc. Also, Linkedin in and Facebook, of course, have groups for people with specific health conditions.