Does your community have a "community message board" maybe at that big intersection in town that you are able to get a spot on? You may want to check that out. Our local area has one such thing that, I believe, is sponsored by local businesses for anyone to "advertise" their event on.
newspaper, signs around town, flyers at local places, letters to parents, word of mouth, etc...
We're also doing incentives to get parents to come. Our attendance was low last year, so we are doing special prizes and also teacher incentives; for example, the class with the most parent/guardian attendance at the auction will win $50. Another is that we auction off "street signs". We auction off 1 sign and do a raffle with the other. You MUST be present at the auction to win the raffle, so hopefully they'll stay and buy. Hope this helps!
Good luck with your auction! We're gearing up for ours too.
If you're drawing from the same pool of families then I would try to broaden your pool.
We have a local newspaper that we put an ad in.
Another school near us puts up a professionally made wooden sign by the roadway.
What have you found to be the most effective way to advertise your auction. We have 6 schools in town who all do them, 5 are done in the spring. Lots of competition drawing from same pool of families.
Besides word of mouth and flyers home via backpack, what other avenues do you use and what has worked best?