Try to open contests with prizes. It also useful to give $1 to give to every affiliate that join. Just to make little attraction.
Now the latest trend to attract thousands of affiliates is simple costs very less. Find some one who has more than 20,000 followers on twitter related to your niche and then contact the owner of the profile for a small amount in order to tweet your message for affiliates to promote your product. Gather has many twitter follower owner has possible and ask them to tweet your offer with a link , keep track of the people visiting your landing only from twitter and try to optimize it next time. Doing this is a piece of cake,this is my own strategy developed to gain more affiliates. Also contact super affiliates in your niche to promote your product. Collect your affiliate email address next time.