Approach in writing groups of people, outlining a proposal of what you want to do.

Place ads in Loot/university groups etc.

Virally organise a meeting through word of mouth and technology.

err set a camera up and start filming in the right circumstances.

You could join shootingpeople which costs a few pounds to do.
actors will just have to act themselves and a role. Though it's very hard for actors act real.

Animation or pupetry might be your salvation?