[heroic]

Are you asking them to give them their email ids, etc to you? If yes, then why don't you email users who haven't used the app in a long time, about news features, etc and also include a feedback link there. You might get some responses.

Also, try to find the uninstall rates for other todo apps. I personally in a moment of self realization decide to make todos, but the very next day I get fed up and uninstall the app, maybe thats common across a lot of users?