Surface plasmon (SP) waves have been studied on a wide range of geometries and at frequencies spanning from the visible down to the radio spectral range. In particular in the terahertz (THz) spectral range, SP waves confined on metallic surfaces have been widely investigated for their potential applications in THz photonics. I will demonstrate several new routes towards realizing active control of THz plasmons via influencing SP nanometer transport with external stimuli. We describe a new mechanism for ultrafast active control of plasmon propagation. By using time-domain terahertz spectroscopy, we demonstrate that electron spin state can influence plasmon propagation. This phenomenon is similar to the electrically-driven spin accumulation phenomenon resulting from current transport between F/N layers. With this first demonstration of the merger between the plasmonics and spintronics fields, we envision the realization of a new class of ultrafast spinplasmonic devices having unique functionalities.