As an accountant, I get approached a lot to help with formulating business plans for potential investors. This also includes, introducing the business owners to new investors, potential investors, long-term investors, and angel investors (if I can find them).
When I approach any individual, I like to start within my own circle first -- high school friends, college classmates, and chamber of commerce. Once I have identified my initial roaming area, I then classify the "investors" into "New Investors", "Potential Investors", "Long-Term Investors", and "Angle Investors".
The reason for such categorizing -- so I know how to approach and what to approach them on.
-- this is likely to be their first investment and they will range from terribly reserve/conservative to being very liberal with their investment. They are likely to care more about the infrastructure of the business and because this is their only investment right now, they are likely wanting to be a part of the business on a more active level (weekly financial reports opposed to monthly or quarterly).
-- I approach these investors according to my profession. I am an accountant and have an established reputation for careful money management and working on a tight budget to make a company successful. I also have a reputation for "not needing a large client. I will make your company into a large client". Thus, they have confidence that an accountant with such reputation is going to watch their investment.
-- These investors already have other investments and are just looking to diversify their portfolio. They likely won't want an active role in their investment due to the quantity of their investment. They are also a slightly older crowd and have their own accountants & financial analyst on reserve somewhere on their phone.
-- Approaching these investors require more skills, but the payoff is bigger -- more money, more resources, and they're ok with being absent from their investment. However, they'll definitely want to see you polished up, suit and tie, and at least a good level of assurance that you're not an "upstart kid looking for money" as one of them had told me. Approach them as you would a new investor -- just expect to have all the questions answered, good responses, and a lot of projections.
-- These investors are normally older and you will likely be dealing with their accountant(s) than you will with them. They are old money and have been investing a long time and thus, are highly experience and can smell a good business plan when they see one.
-- When you approach these type of investors, approach them with significant care. You are not only presenting to them, but also to their accountant/financial team. They will bring the idea back to their accountant and relay it, which means, anything and everything you say have to be extremely clear so not to be lost in translation. Also, copies of business plans, projections, investment amount, and so on is your best bet. Finally, if you know a friend or a family member who knows this type of investor, it is going to be your best approach.
Now that we have the type of investors out of the way, finding them is not that difficult. Chamber of Commerce is a great place to meet business owners and investors. Also, approach your local investor's organization -- there are about 10 big ones in St. Louis and I just did a quick search. Approach friends and inner circles. Failing all of this, go to a Financial Analyst or Accountant that you do business with frequently. They are the money handler and will know who is interested and who isn't.
Anyway, I hope this all helps!