20 years ago, fundraisers for various causes realized that it was hard to get people to make a donation. So they invented the "Walk for Whatever" format — go out and get your friends to pledge so much per mile. It was a great idea — it made it fun to participate and fun to raise money. And you didn't actually have to talk to your friends about a disease.
But it's old now. It still works, but nobody is excited about it. It's a common problem — the novelty has worn off and word of mouth is running out.
What do you do? Find a new word of mouth topic.
Ideas: Train participants to run a marathon (Memorial Sloan-Kettering's Fred's Team) or Bike Naked.
Lesson: Word of mouth needs novelty. When people stop talking about you, look for a fresh reason to have a conversation.