The better you know your audience, the easier it is to find content that will go viral.
Take as long as you need to determine what audience you're after.
Based on what you intend to promote, such as your product or service, look for the kind of people who interact with those types of products or services.
Try to figure out your audiences:
CPA / PPD Offers?
If you'll be running CPA/PPD type offers, the only way to know which audience is best is by testing out some campaigns.
I suggest using Fiverr to help you create an ad, otherwise use your own video/image software to make an ad.
Then find an influencer in the niche you're interested in trying and pay them to run a promotion. You can find influencers either directly on Instagram or through Shoutcart.
Search for the hashtag of the product to see what kind of influencers are using that hashtag.
Read through comments to see what kind of people are interacting with the content.
Search Facebook for your products to find the most engaged posts. This will give you an idea of the type of audience you want to go after.
Search through hashtags in your industry and find accounts that get the most engagement
Look at other influencer stories
Often influencers will post ads in their stories. If you're interested in a particular niche, look at other influencer accounts to see what they are promoting. If its products or offers you intend to promote also, then thats something for you to note.