To get higher participation should start with just a photo contest. Have people take a photo of themselves near a known landmark of their city. Facing camera, or from behind optional, since some people are private. Then if people choose they can expand on their 'map marker' with a story.

Personally I find initiatives here like "Twitter madness" over demanding and those tweets are doomed to get drowned out.

This one has potential to have a lasting effect though since as that map grows with participants it paints an instant collective picture of users here. Then a person can journey through the world and see/read more.

KIS - keep it simple!
Is always the superior way at first.

That's why reblog and comment is what people did more because it's a simpler way of supporting over actually following the requirements.

Good luck!