Be very careful with any of the stronger solvents such as acetone and lighter fluid. They will dissolve the glue, but when they evaporate off you will find that the glue will have been spread over a wider area and in the meantime the solvent WILL have attacked the plastic surface. Something like 1,1,1-Trichloroethane would be ideal, which used to be available under a number names such as Genclene - but you would probably find this even harder to get than acetone.
I have 2 methods that I have used successfully for a couple of years (i.e. ever since my 5 litre can of Genclene ran out!).
One is a small bottle of Mangers' De-Solv-It which I bought from a DIY store. Useful for lots of different stains and also removes label residue very well. Try B&Q or a wallpaper shop.
The other is gaffer tape. Any strong self-adhesive tape will do. Stick it on the glue and peel it off again. It may take several goes but the glue will stick to the tape and peel off with it. This is my preferred method for removing label residue from CD cases. And unlike acetone or lighter fluid you can even smoke while doing it without losing your eyebrows!
Norman