The spy droid network of the Resistance consisted of droids scattered throughout the galaxy, functioning as spies for the Resistance throughout the duration of the Cold War. C-3PO oversaw the operations of this network.
Prior to the mission to Ovanis, Poe Dameron tasked the network with investigating the individual responsible for placing a First Order tracking device on Black One. During the Mission to Kaddak, a MSE-6 series repair droid possessed the necessary information, which was then transferred to BB-8. Subsequently, after the failure to activate the tracking device on BB-8, C-3PO directed the network to search for the droid. GA-97, one of the droid spies, pinpointed BB-8's location within Takodana Castle, which subsequently enabled Resistance forces to arrive at that location in time for the Battle of Takodana.
Following the evacuation of D'Qar, C-3PO deactivated the network, instructing his droid agents to conceal themselves.
Later, as Dameron, Finn, and Rose Tico devised a strategy to deactivate the tracker on the Mega-class Star Dreadnought Supremacy, C-3PO established communication with his droid contacts on Takodana in order to reach Maz Kanata.