I have spend nearly 10 months in my start up where we developed an android application which was recently bought by a company. As a founder I lead the team. It was not a registered company, but our application has 1.8 million users (which is now transferred to the buyers developer account). Can I add this experience in my resume?
Of course you can. Any relevant experience you have belongs on a resume, whether it was working for a registered company or not. In this case, I'd list it just like you would another position, and include its acquisition as a bullet point beneath, or perhaps in parentheses by the end date.