As the comment by 'pja' highlights, most of the restrictions to such an approach are legal.
The least restricted market in this regards is the United Kingdom where there are quite a few businesses in the crowdfunding/peer-to-peer lending space already - for equity funding see Seedrs[1] and Crowdcube[2].There's even instances of SMEs raising equity from the public directly e.g. Brewdog[3].
The UK regulator (FCA) is just catching up so things may change next year[4].
[1] http://www.seedrs.com/ [2]: http://www.crowdcube.com/ [3]: http://www.brewdog.com/equityforpunks [4]: http://www.reuters.com/article/2013/10/03/britain-crowdfundi...?