Marseille is the second biggest city of France, located in the south.

Hitchhiking out

Going to Marseille is usually easy, but out of it, might be a bit more complicated, as there are many highways crossing nearby.

North by A7, towards A8, Aix en Provence, Lyon, Montpellier or Nice

You can try at the roundabout near the Arc de Triomphe - Place Jules Guesde. That is where L'Autoroute de Soleil (A7) starts. Place yourself just before the highway begins, still on the roundabout.
If you do not believe in your patience it might be better to go by bus to Aix en Provence (4 Euros) and from there either to Avignon or to Nice.