Do you want a tipping point online? Do you want e.g. an online community to self recruit and grow all by itself? This is not as difficult to achieve as you might think. Creating an online movement is beautifully illustrated by +Derek Sivers in the media clip below.
The thing about tipping points is, it varies based on fluctuating criteria (such as quantity or quality), but remains the same with respect to a few simple principles. Do not mistake criteria for principles, and your experience will be like mine. For instance, keep in mind:
Principle # 1: An online tipping point is preceded by intensely focusing on one idea.Over the years I've created several movements. Every one of them grew by carefully selecting a focus. To create an online movement it helps to be unique in a niche area, preferably the only one, if you can. Once you've found your focus, search for the right people and invite them to invite others. Then, stick to it on a daily basis and repeat until you see exponential growth.
Principle # 2: An online tipping point occurs when the self interest of the target group is met.People are driven online to obtain some kind of (selfish) objective. The best way to effectively make use of this is by indirectly serving them in that particular need. Don't just start something online without thinking this through. Know the need, then do what you do to fullfill it, and users and members will come running.