How do I start a knowledge management system when people are not interested to share information?

Very good question, regarding the more general problem - how to build something that people will use.

In Wisdio we have learned a lot and we are still learning. And the main lessons is that the standard ways of management business are not applicable, because startups are organizations not for executing plan but for learning what users want.

The best way to understand it is using The Lean Startup method. It is based on build-measure-learn cycle:

The key point is keep this cycle as effective as possible. To do this, we have find ways to test our hypotheses quick and at lowest possible cost.

Now, the question becomes to mind: what is this hypothesis? We should look at it as a complete business model where the key parts are: the problem we are trying to solve, who is our potential user/customer, our unique value proposition and the solution we are going to provide. The excellent way to sketch complete model of our business it to use The Lean Canvas, based on Alex Osterwalder’s Business Model Canvas and optimized for startups.

So, to come back to your question, how to start knowledge management system. 

• First of all, think what and whose problem do you want solve (fill in Problem and Customer segments field)
  
• Next, find out what do you offer to your potential users (your Unique Value Proposition)
• How do you plan to that (Solution) and why your product will be unique (Unfair Advantage)
• The next key questions are: how will you make money (Revenue Streams), how will you find users (Channels) and how will you measure your progress (Key Metrics).
• And you should not forget about calculating how much money do you need to make it possible (your Cost Structure).

And now, when your canvas will be filled in go "outside the building" and discuss it with your potential users! It would be also valuable to show your idea to some experienced advisors.