Paris is the capital of France.
Like nearly every big city, it's difficult to hitchhike out of it. Paris is even more difficult, since the ring highway (periferique) is relatively small.
Take RER B to Stade de France and after walking a while you'll find a final traffic light where you can ask for the first gas-station on the motorway (around 2km away and NOT accessible from outside of the motorway)
The first gas station is close to RER A station Bussy St. Georges. From there you walk south for about 1 km (you can ask at the counter) along a bigger road, which will lead you to a roundabout. You can try from there, but the gas station is just a bit more than 2 km from there. You can walk on the grass field next to the highway. The gas station is called "La Ferrière". An alternate route to reach the gas station is to walk through the industrial zone of Bussy, right south of the railway, then reach the bridge over the highway and then follow on the grass until the gas station that is quite near. This avoids walking in the grass (annoying especially in winter and when raining) and instead most of the walk will be on a road, and you will save some time. You can follow this route on Google Maps - the gas station can be seen right of the bridge on the south side of the map.
The péage is not far from there, though it might be further than the closest highway exit...
Porte d'Orleans, at the periferique seems okay, Metro Porte d'Orleans. There's a gas station, and a good spot at the traffic junction to the "perfiferique exterieur". Don't go with cars going into the suburbs. The next tollway or gas station takes about 50 km!