If I create an app with social logins and the app have huge amount of data, are these data under the social login company hands (for example Facebook), can they use it or make whatever they want with it ?
And does the app that has a social login affect the ability that someone may purchase it for example can Google buy an app that has Facebook login ?
Or it is not worth it and I should create my own authentication system ?
Thanks in advance.
You should read the privacy policy. Most of the times they don't use the information if user doesn't accept that it can be used. Some companies use the information without referring to the specific user information like email or name, but they may use it for getting demographic statistics.
If your app has only one social login is your own choice, but since social login doesn't make your app belongs to the social website, there's not problem for other company to buy the app. But it is always recommended to include a developer login and to leave space in your backend to connect to other social media. For that specific case I think that if Google ever buys your app they will pretend to add their own login.