I'm not a big advocate of stealth :) I prefer not to be but it's not an option unfortunately in this case.
Complete the following sentence Stealth has developed or is developing .... that solves the problem of ..... for ......
When completed you should be able to identity venture capitalist firms who wish to and or have made investments in that space. Corporates are more problematic if your reasons for stealth are to avoid the industry they are in. Angels are also problematic we typically syndicate which raises more possibility of them doing due diligence where you might find your cover blown.
Hope this helps
Check Angel investor networks (like https://angel.co/), find investors contact details and try to contact them privately.
If you are starting up a company that might be in direct conflict with your regular company you will need to set up a corporation let's say in Hong Kong so there is no likely tie to you. But outside that for a moment I like to start up companies on a shoestring or at least test out the concept on real people which a have a couple of methods of doing that. Investors will fight over a proven concept but on just speculation you have to fight to find them. If you need help testing out your idea I can help, thanks...Ken Queen