How to start building a social network that links into Facebook/twitter like foursquare (but not location)?

[Baba]

I agree that social media and user-driven content is on the rise. However, you are still competing with some pretty big boys. The first thing I would do is work out a business plan. Hire a consultant to help you put it together for investors, because you will surely require financial assistance when the marketing aspect comes into play. At that point, you will have to go viral, create a real buzz via social media (Facebook & YouTube, maybe also Twitter & LinkedIn), and invest heavily in back-links to rise in search engines. This is known as the link-building process, the most critical (and more expensive) part of SEO (Search Engine Optimization) - getting your site ranked in search engines. Once you are in contact with other business consultants (i.e. to put together your business plan), create a NDA (Non-disclosure agreement) to protect your ideas.

Then, I would sit down with a business analyst to create all of the instructions for the programmers (programming language could vary - PHP, CSHARP, Perl, Java, Microsoft/.NET technologies...). *If your are looking for investors, most large corporations trust .NET technologies.

See the various resources I have included (below).
Also, some articles