Very hard to solicit investment this way. Very few legitimate investors will need to be on forums looking for deal flow and most receive 100s of proposals per day.
The best way to find investors is to find their gatekeepers - these are the people that the investors has worked with in the past and trusts. These can be CPAs, Lawyers, other business owners, portfolio companies, etc.
Most investors see so many business plans everyday that no one really stands out or above the other. But, if you are recommended from a trusted source - then, your proposal will be moved to the top of the pile and given a bit more consideration.
To find these gatekeepers - you just have to go where they are (very similar to marketing your product and going to where your customers are).
Small Business & Start-Up Financing