Not everything is a technical problem. If there isn't a place as of yet like an online network for entrepreneurial people, it is not because no one was able to do a site or a forum where such people can hangout.

There is chicken and egg problem at play here.

If I had designed and launched a site exactly similar to HN or Stack Overflow, it would have been empty and dead, even if it would look exactly the same. The reason those 2 worked was becaue those that started it had some number of followers already to get the ball rolling.

Just my 2 cents.