South towards Resistencia
Take a Bus #25, it goes to Villa del Carmen but you need to go out earlier (cost 8.5 peso, need card SUBE, see "Other useful info"). You can find a lot of bus stops on Av. Dr. Luis Gutniski or Av. 25 de Mayo. About 3 km after Airport you will see Petrol Station Shell on the right side, and you need to go out from the bus after 300m, near Police Control (-26.240009, -58.248696) and you can hitchhike just there.
Places to avoid
Be careful in "Comunida B° Nam Qom", located on the North-West of Formosa. It's a settlement of poor indigenous groups the Toba(Qom) people.
Other useful info
You need to buy a transport card SUBE, or ask passengers to pay for you with their card and you give them money. You can use card SUBE in other Argentinian cities.