I'm the Foster Coordinator for a medium sized shelter in Northern Minnesota, we have about 100 current fosters. The best recruitment tactics that I have used are using pictures of animals currently needing foster and being able to send those animals into foster directly after the training. We have about 20,000 followers on Facebook, so I post occasionally on there, but I also utilize our weekly radio and TV slots. One of the best ways to get new fosters is through word of mouth, utilizing your current foster and volunteers. I often ask my best fosters if they have any friends or family that are interested because I want more of them! We also have a short online application so people can apply while their interest is highest, I usually follow up within 48 hours and offer training one-on-one whenever possible.
We also have an amazing foster manual and I would be more than willing to share!