I'm an artist that did a concept design for one of my mobile app ideas, and I've met a company/developer that can develop the app for a certain price quote, which I just can't afford now. Due to my lack of the funds, I've reached out to about forty venture capitalists(VCs) through the LinkedIn site, but have been unsuccessful to raising the funds through them. Even though about four VCs showed interest to my app's concept and asked for my business plan etc. they seemed to lose interest when I sent them my business plan without any explanations.
I'll appreciate if you can advice me on the best possible way that I can raise this fund through VCs/angel investors to enable me develop my idea into an app that can be sold at the app store.

It's simple. They lost interest because they saw no way to make money off your app idea. So your app either isn't a money maker, and not worth their time, or you're not pitching it properly. That's something that has to come from you, and not something anyone else can help you with.

How are you pitching this app? How are you promoting it?

Apps are a dime a dozen, every second person has an idea for a new app. In order to make money off of it, you have to show that it's worth the investors time and money.

You're one in a billion, literally. How are you standing out? What makes you special? What makes your idea worth investing in?

If you aren't detailing the function of the app (probably for fear of theft) how do you expect them to judge its marketability?

What you need to do is prepare a non disclosure agreement for them to sign before you reveal the details.

Patent your ideas first before you pitch them.