After Seymour's croaking made Lola mess up her makeup, she decided to take care of the problem herself, or at least Lana thinks. It is unknown if he was real or not, because in the end, it turned out to be a prank for Lincoln set up by Lola, because he was using noise-cancelling ear buds, and the flashbacks could have been fake or real.
Despite the stories being made up, it appears Seymour may have actually been real. Seymour's name (which was misspelled as "Seymoor") was taped on a tank that Lana kept him in her room. After the story to the frog fiasco ended, it's shown that Seymour's name was covered up by a label for Lana's new lizard Izzy. Lana still seems to hold some feelings of despair over the loss of her frog, and hates to bring it up.
Considering the frog fiasco was made up, it is likely that Lola never did anything to Seymour, as Lana admits she can't prove she did, and his true fate is currently left unknown. Whatever really happened to the frog remains a mystery.
Seymour is a standard looking green frog.