Google could be a good place to start searching for the information (s). Just be careful about the authenticity of the data that pick for your business plan. One way to ensure authenticity is to pick data published by established brands.
However, given my experience working with plethora startups around business planning, I am curious to understand following:
1. Why do you need info on Mobile App revenue?
If you're trying to hinge your Apps' ability to monetize on generic industry numbers then you're on a shortest possible path to getting your business plan scrapped.
Alternately, in case you aren't clear about your financial numbers then it isn't a good practice to reverse engineer your numbers by looking at revenue figures of other applications.
Thirdly, if you're counting info on mobile app revenues as a data to be mentioned under market research/analysis section then again it could be a bad idea. The data should provide an insight around your application concept and business idea.
Do feel free to reach out to me for any further help that you may need. I am just a call away to be able to provide further clarity. Thank You!!
VisionMobile / DeveloperEconomics
Their blogs and their reports. Definitely worth it.
Appannie provides great intelligence stuff / per domain, though quite expensive.
They bought Distimo which was the other source: http://www.distimo.com/appiq
In Localytics resources, you'll find interesting things: http://www.localytics.com/resources/
Hope it helps!
It basically depends on what type of data you want and for what type of app you want it. For iOS apps, extracting estimated download data is possible using XYO.net. It also works for Android but I have usually seen that the results generated by XYO are those of the latest app update and not the cumulative data for all the updates of the app.
With regards to revenue and other data, such data might be disclosed by the app company itself on their corporate and media kits or as press releases to showcase growth in revenue, but such data would only be available in public domain for extremely popular apps.
The best way to perform market research and pitch to investors is to go into the market and see who are your competitors and similar apps. Then analyze their marketing strategy, # of downloads, revenue (if available), when the app was first published etc. Along with this, you should also try and evaluate what your app's marketing strategy will be, whether app store optimization, advertising, PR etc. and then try to match and improve your strategy with that of your competitors.
If you have any questions or want more details, hook me up via a call and I'll be happy to help!