How many Employees are working in .. Facebook, Twitter, Tiktok and WhatsApp

Development might look easy for normal people, specially developers who just learned how to make forms and pages, which makes it look as easy as making a watsapp app or twitter app, since if you look into it there is nothing there that looks that complicated, it is just a pages and forms decorated with information that we understand! and because of that making a company out of this is just as simple as bringing more people making forms and pages! so lets see how real companies do in real world in terms of how many staff the took in to make the job done