Nothing is so difficult, but it needs good planning. In the company I currently work we're developing our own social network. The coding is too much if you choose to have a public API for 3rd party developers, and scalability in mind. If you want to scale to maximum you need to consider a smart architecture. In our example:
- Front end (the main website) -> Laravel (PHP) for rendering pages (HTML/CSS/JS/LESS etc...)
- Back end (for every single request) -> NodeJS, MongoDB & express.
- Android app -> Java, iOS app -> Objective C
We currently have like 8 developers (and one of them is our CTO). We have a designer, a community manager and a product manager (CEO and CMO excluded from the list). And imagine we're startup.
It's more about the money for the infrastructure rather than the development itself.