I'd run a lead ad targeted towards people with similar job titles or at competing companies. Include relevant job information (title, salary range, etc), then promote the ad as "easy application" and require full name, email and phone. Once they apply, send an email requesting their resume or get them on the phone. I work for a digital ad agency (AdvertiseMint) that specializes in Facebook and Instagram ads, we could help you set these up if needed. - Brian
This really depends on the job and market you're targeting. Like the other poster said you can target job titles at competing companies. You can target interests related to the business as well. The ad is critical as you want to ensure its optimized for performance
Look at the major brands and what they use and do the opposite. You need to write your ad as if you are speaking to only one person at a time. That person is your idea candidate. Just pretend that you could say something like this, "Hey Bob Smith, this is the perfect job for you. Read this ad and I know you will agree." Of course you can't do this, but you can keep in mind that you are focusing on one not the many. Secondly, write out at least 20 reasons that this candidate would want the position and try to get at least the top 3 in your ad.
I hope this helps.
Best of luck,