My daughter got biro on our suite and I tried literally everything I could think of but the only thing that removed it was continual buffing with a clen duster. This took ages so is no 'quick fix' but it does come off eventually.
You could try a little milk on a soft cloth.Another method is hairspray.Spray on and wipe off quickly. I found this in a book of household hints.
But....try on an inconspicuous area first because it will depend on the colour of your sofa.
You can buy a ink remover stick for leather, its like a waxy stick. You rub on to the mark and it comes away. Or you can try a bit of vaseline petroleum jelly with a soft cloth, it works but the stick its better.