Many of us actively use sites like Twitter and Facebook to promote our businesses. And those of us looking to connect with more business-related contacts may turn to sites like LinkedIn to develop relationships with people we have worked with or may want to work with.
With the growing use of social networking by business professionals, there is a growing number of social networking sites focused on business users and meeting their needs. Here is a list of 20 social networking sites for entrepreneurs, business owners and professionals that are worth a look.
Biznik – A community of entrepreneurs and small businesses dedicated to helping each other succeed.
biznik
cmypitch.com – A business website for UK entrepreneurs to get quotes, advice and more.

cmypitch
Cofoundr – A community for entrepreneurs, programmers, designers, investors, and other individuals involved with starting new ventures.
cofoundr
E.Factor – An online community and virtual marketplace designed for entrepreneurs, by entrepreneurs.
efactor
Ecademy –A business network for creating contacts and sharing knowledge.
ecademy
Entrepreneur Connect – A community by Entrepreneur.com where professionals can network, communicate, and collaborate with others.

entrepreneur connect
Fast Pitch – A business network where professionals can market their business and make connections.
fast pitch
Focus – A community focused on helping business decision makers and IT professionals make decisions.
focus
JASEzone – A professional community where you can find potential clients and business partners.
jasezone
LinkedIn – A professional network that allows you to be introduced to and collaborate with other professionals.

linkedin
Networking for Professionals – A business network that combines online business networking and real-life events.
networkingforprofessionals
PartnerUp – A community connecting small business owners and entrepreneurs.
partnerup
PerfectBusiness – A network of entrepreneurs, investors and business experts that encourages entrepreneurship and mutual success.
perfectbusiness
Plaxo – An enhanced address book tool for networking and staying in contact.

plaxo
Ryze – A business networking community that allows users to organize themselves by interests, location, and current and past employers.
ryze
StartupNation – A community focused on the exchange of ideas between entrepreneurs and aspiring business owners.
startupnation
Upspring – A social networking site for promotion and social networking.
upspring

XING – A European business network with more than 7 million members.
xing
Young Entrepreneur – A forum-based site for entrepreneurs and small business owners who are passionate about promoting business for themselves and others.
young-entrepreneur
Ziggs – A professional connection portal founded on the principles of professionalism and respect.
ziggs
Do you have any other social networking sites for business that you use? Which one has worked the best for your business?

Details taken from  - http://www.sitepoint.com