Hardly an exhaustive list but some useful sources, background and inspiration below:
Statistics
How many people use top social media, apps and services?
The 7 most interesting social media studies and what to learn from them
By The Numbers: 25 Amazing Facebook Stats
By The Numbers: A Few Amazing Twitter Stats
Demographics
A demographic portrait of Twitter, Tumblr, Pinterest, Instagram and Facebook users
Who uses which social network. US-based demographics
Searching and monitoring social media
Searching social media? Don’t miss what’s hiding in plain sight
Developing a social media policy
Social media: copyright and fair dealing
How to use Twitter
Twitter for the Newsroom
Channel 4 News’s Faisal Islam’s top tips for digital journalists
How to use Google+
Eight Google+ tools for journalists
How to use Facebook
Best Practices for Journalists on Facebook
INFOGRAPHIC: How Facebook’s Graph Search Will Change Digital Marketing
How to use Pinterest
10 Innovative Uses of Pinterest
How to use LinkedIn
Top tips for journalists
Top 10 tips from 10 best LinkedIn Company pages 2012
How to use Tumblr
So who in news knows how to use Tumblr?
Blogging
Ten years on, how to make the most out of Facebook
How to write a successful blog that also promotes your business
RSS feed
Twitter
LinkedIn