Marseille is the second biggest city of France in the South. Hitchhiking there is nearly impossible
Going to Marseille is usually easy, but out of it, it's very hard because of the way they made they made the highways there. You can try at the roundabout near the Arc de Triomphe, but I wouldnt wast my time. It's better if you go by bus to Aix-en-Provence (4 Euros) and from there on the Routes Nationales either to Avignon or to Nice.