A tale of 4 social networks

I got interested in investing in the stock market when Twitter (NYSE: TWTR) when public with it's IPO in late 2013. When the stock first started trading it shot up to approximately US$72.00 in the first day of trading. This was too expensive for me to buy. My first investment was an oil drilling company which I sold about 4 or 5 months later for a small profit. I have made a number of investments since then. However, this post is not about investing specifically but who or what are behind 4 social networking sites - Twitter, Google, Facebook and Instagram.