Wouldn't this photo be a great conversation starter?
You could hang it on the wall in a room in which you want people to talk to each other and have a rock-tumbling noise playing in the background. Or you could carry the photo in your purse and then whip it out at just the right moment when conversation is lagging. You could take it to parties and pass it around, asking other party goers if they've seen this person or if they can identify the rock. You could send an urgent email to your family and friends telling them that you are organizing a bus trip to go help this brave, tired guy hold up the rock and plea for them to sign up.
Another site, conversationstarters.com, suggests (apart from the rock) other ways to get people talking: