Look at the Work Sharp Knife and Tool Sharpener. Supposed to sharpen serrated blades. I've used it on serrated blades with some success. The belt is too big to get into the smallest serration but it will sharpen the larger serration on the blade. There's some videos on how to use it. Sharpens regular blades really well.
I have that sharpener. It has a guide for serrated blades, but the instructions say to only sharpen the back side, using the guide, not the serrated side. Seems to work on my serrated blades using that method.
And I just have to say, I LOVE the Work Sharp Sharpener.