Need more users for my internet startup (Growthhacking) (High churn)

If you're just starting out, then naturally you're going to focus on getting users in the first place, and not how to retain them. That's fine.

However, quite soon after you've launched and first users join start thinking about retention. Retention is just too important to ignore. If you have a hole in your bucket, what do you do? Run faster so that less water leaks? No. You fix the hole.

Maybe below video makes clear how important retention really is:

Habits are extremely powerful. Once your users got used to your product, they don't want to miss it anymore - and will not churn. 

Therefore, be quite generous with how much access you give your users to your product so that they have enough time to form the habit. How long this takes depends on the product, however a good rule of thumb is 30-45 days. The good old "30 day free trial" (which is as old as the software industry) is based on this principle.

If you want people to use (or share) your service then learn what makes people tick by reading good books on psychology. 

A great primer (also for advanced marketers) is Robert Cialdini's "Influence". Buy it here and never look back.