For etching acrylic, you can use methylene chloride. I said you could, I'm not sure if you'd want to. I'm not sure if methylene chloride will attack the plastic laser printer toner is made of, wikipedia says it's styrene acrylate copolymer or a polyester resin, so you'll have to find out what you're dealing with before you can check those. Sounds to me like styrene acrylate copolymer is too similar to polymethylmethacrylate (which is what Plexiglas is) for you to find an exclusive solvent.