Why App-User Increased like Virus Spreading

There are many ways that an app can attract users, but the one we shall pay more attention is the sharing by the old users. Sharing happens at any time. Likedin, a professional social platform, obtained substantial amount of new users via email invitation by old users.
Apps have adopted different ways of sharing, but which way will work on the users?  let’s take a look.  
1.潮流或有趣的APP内容分享。Trend or interesting app content sharing.
People will share something when it represents a trend or it is interesting, for example, when the shared bikes just came into our life, people would share the riding time and distances via the app as it is new and trendy. In a short time, the sharing brought the shared bike company large amount of new registrations.
2. Stimulate sharing via promotional activity
Cash return, coupon, and gift money (red packet) can stimulate user sharing. For example, a food delivery app acquire new users via the sharing of red packet by the user after the delivery is completed.
3. Share with friends to play the game.
Sharing is also very common in games. In some games, when your health points are running out, you can ask your friends for help, but only when they are the users can they give you the health points. So after the health points giving is completed, the game acquires new users.
4.  Sharing for value added service.
After the basic needs of a user have been satisfied by a product, the product company may offer some value added service, and by sharing or recommend the product to friends, the user can have the value added service. For example, an education app allows the user to have a time extension for the tutorials after sharing, and this is the tips for user base building.
For products at infant stage, sharing can make substantial contributions to traffic surge. Besides offering better user experience, we shall offer promotional activities to urge the users to spontaneously share the products, thus the amounts of users will definitely soar.