We made test campaigns with Facebook, Instagram, Google AdWords, Youtube, Twitter, Badoo, Tinder, WeChat, Telegram, any suggetions what else to try before to go deeper in the most efficient one?
Who says that social channels are right for your app in the first place?
When advertising, you need to know both where your audience is, and when they are considering things like your product. If they are only on social channels for entertainment and aren't thinking about their health while using social media, then it's the right place but wrong time. You have to have both conditions. What did your marketing research tell you about how your prospects discover health apps? Did you validate that your prospects want to find out about health apps through social channels. Running ad experiments isn't enough. You need to talk to prospective customers and learn what they're doing now to discover products like yours, when they tend to be looking, and where they trust the information to come from. If you aren't aware of those factors, you've missed a key component of your marketing strategy. Just picking the best of a collection of bad channels is not the way to advertise.
Maybe the right place to advertise is in ride-alongs with other health products. Can you get your flier inserted with local crop share deliveries, with orders from bike shops, with welcome packets from gyms? Be where your prospects are when they're thinking about their health, not just where there's a large audience you have to wade through. If your customers typically don't pursue healthy activities, maybe you can get doctors' offices to recommend you to their patients, be distributed by pharmacies, or offer an incentive program for nurses to enroll patients. I don't know your audience, so you'll have to make the decisions.