Any alternative wouldn't be that different from today's Facebook because when common users looks for social media platform they will always go to the one with the higher users base, most of them at least will do. Number often win on quality in that context, especially when money can buy well crafted PR campaigns. Pay a thousand handsome guys/girls to appear there, get some popular actors/bands on board, create contro…
The higher user base is important that´s right. But pay them to join might not be the best way. I would say, you need to analyze Facebook and their weaknesses. Then aim to solve those weaknesses with your product and use such failures of Facebook like last weak to convince Facebook user to join your product.