LinkedIn: ESSENTIAL. Everyone should have a profile with a photo.
The world's number one professional networking site with more than 100 million accounts, LinkedIn has become the place where people expect to find everyone and if you are not there it looks strange. Just having an account is not enough. There should be a medium-length profile and a photo. The photo is important to identify people where there are several with the same name and helps reassure people you are real. If you have time you can use the Groups feature to build relationships, too. My LI profile is at http://fr.linkedin.com/in/andrewhennigan
GooglePlus: IMPORTANT. Create simple profile with photo and watch for interesting people.
Launched to the public in September 2011, GooglePlus is a rival to Facebook that has a much more professional look and feel. This is a good place to have a profile because it looks like you are keeping up to date and because it will soon be a major player in professional networking thanks to integration with other Google products. Through GooglePlus it is also easier to engage with influential people than in many other networks and the level of trust is higher because of the real name policy. My Google+ profile is at https://plus.google.com/105057073153150809821/
Facebook. NEEDS ATTENTION. Either hide your personal profile or clean it up.
Most use Facebook for personal conversations but an increasing number use it also to stay in touch with people who can help in their career. This is much easier thanks to the introduction of features that allow you to address your posts to people in specific categories or to subscribe to people who are not "friends". If you plan to use Facebook for work-related networking make sure you remove or hide all the photos of you with beer in your hand before you allow access. If you plan to use it only for private conversations then make sure it is not visible in anyone in a search. Even if you use Facebook for private things you should still let your friends know about what you do and what you need; maybe they can help. My Facebook profile is at https://www.facebook.com/andrew.hennigan
Twitter can be an excellent tool for discovering and engaging with people who are useful in your professional life (see How to Use Twitter for Professional Networking), but it only works if you have time to follow tweets and to respond to people. If you don't have time don't bother -- dormant or automated accounts are ineffective -- and never mix private and career tweets; if necessary have separate profiles. For your professional Twitter profile use your real name and a recognizable photo of you, not your cat. My Twitter profile is at http://twitter.com/andrewhennigan
Zerply: RISING STAR. Create a profile with carefully chosen tags
One of the new wave of networking sites, Zerply has a very simple, clean, interface that appeals very strongly to digital natives, contrasting sharply with LinkedIn, which has a more "corporate" look. Zerply is new and not yet a household name, but creating a profile is very easy and simply being there demonstrates that you are in touch with new developments. This site is most popular today with people who find the look and feel of LinkedIn old fashioned -- often people who are younger or work in the startup community -- and also people who value good design. Creating a profile is very simple but choose your "tags" carefully because they are the key to being found. My Zerply profile is at http://zerp.ly/andrewhennigan.
There are many other networking sites. Some are popular in local regions -- Viadeo in France, Orkut is Brazil -- and some are designed for a specific audience. Creative people are often on dribbble.com while software coders are often found on github.com. The best way to find these regional/market sites is to ask someone who works in the area or Google successful people and see which sites they use.
For some general guidelines about professional networking see also Three Keys to Successful Networking.
This post is based on content from Professional Networking; How to Plan, Build and Maintain your Network, available as a 60-90' lecture or half-day hands-on workshop. Visit http://andrewhennigan.com/workshops.htm . Personal coaching is also available to help people develop their network or improve their online reputation. See http://andrewhennigan.com/coaching.htm contact Andrew Hennigan at email@example.com or call 0033 6 79 61 42 81 for more details.
Related Posts on Networking:
How to Separate Work and Private Networking
Involuntary Networking: Why First Street is Fascinating but Scary
LinkedIn Etiquette: How to Approach People You Don't Know
Selling Your Ideas: Influencing Your Way to Success
Professional Networking: Five Sites You Should be Using
How to Use Twitter for Professional Networking
Sign Up Now: Joining New Networking Sites Boosts Your Reputation
Zerply: Three Thumbs Up, Two Thumbs Sideways
Three Keys to Networking