I do what's called a simple "reverse journalist lookup".
Step 1: Identify your "sister company". This is what I call a company that is very similar to you but not a direct competitor. Make sure you are different from your sister company. For example You may offer an on-demand snowplowing service (Uber for snow removal), your sister company would be Uber. Make sure your sister company is fairly well known and written about in the media.
Step 2: Go to Google News. Since Google News focused on just news it will only show you results from news outlets. Search for "Uber" (your sister company)
Step 3: All the results you see are journalists who understand your industry because they have written about Uber. Presumably they understand the "on-demand economy" too. No need to explain to them what you do.
Step 4: Using Google Sheets simply research each relevant journalist (name, publication, relevant link to the article you used to find them, email and twitter handle). Try to build a nice targeted list of 20-50 contacts. Takes time but worth it.
Try using different terms in Google news, several indirect competitors, etc.
There are several tools, hacks, and services out there that will help you build targeted email lists. I can teach you how to do it yourself for free. Also your pitch is really important. Happy to chat/help.
That depends on your industry, your product/service, what problem you are trying to solve and who is your target demographic. Answer these questions and do a search on who's writing about this.
Let me know if you would like to chat further about developing an effective PR strategy.