Social Networking Sites

Facebook

I have been using FB since my first year of college. I have heard that even in Africa (lacks of water, food supplies) the people use Facebook by using Google's Wi-Fi Drone system.
One of the most influential and huge social network sites(Definitely first generation a SNS)
After M&A with What's up application(does not make a revenue but has kept the largest user infrastructure).
Now, MOBILE is Facebook's oriented focus and a cash cow. based on their financial statements, Mobile AD Revenue makes up 76% all Add revenue on FB.

Twitter

Micro Blogging SNS that limits each post to 140 characters (I like this idea).
Largest penetration throughout U.S but not entirely a whole world. It was a rising star for a few years.
Saleseforce Co, withdrew the process of buying, but I am expecting good deal for both industries (Mobile network, and SNS section)

LinkedIn

Business Oriented, Corporate Brands, giving potential and current associates a a place to Network&Connect. After M&A with Microsoft, LinkedIn showed a little bit less growth rate from expected mark rate. The LinkedIn has a lot of beneficial outs and expectations for both entry level job seekers and experienced professionals.

Instagram

Social sharing site all around PICTURES and 15 second VIDEOS.
using #HASHTAGS and postings, Mostly Nike puts an efforts on it, I believe the corporation has similar agenda and image with Instagram.
PICTURES and consumers can relate to.
Good for Photographers and picture lovers, but for me who does not,
I would not use for this site at all.