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!