How can a sixteen year old pitch a business idea?

Same as anyone else. People aren't looking to invest in someone who is 'good for a 16 year old'; they are looking to invest in someone who is good.

Nobody can give you funds at 16.

For an investor to come in as part of your business, you need to legally be a director, and in a position to give them equity. Since you;re not legally entitled to be a director until you're 18, then you;re wasting their time and yours.

My advice is to spend the next couple of years demonstrating your idea is not only useful, but people are willing to pay for it. Then when you're at a stage you can form a company, you will be in a much better position to give a credible pitch to investors.

The same as most others: spread the word through both standard and online media (perhaps develop a specific site requesting donations) to attract attention. If your idea is solid, someone will most likely give you a monetary boost.