Resonant and leaky-wave THz reconfigurable antennas based on the propagation of transverse magnetic surface plasmons on graphene sheets are proposed. Reconfiguration is achieved via electric field gating, which allows the dynamical control of graphene complex conductivity. The first presented antenna is a miniaturized frequency-tunable resonant dipole with almost constant input impedance upon reconfiguration. The second design consists of a sinusoidally-modulated leaky wave antenna which provides beam scanning capabilities at a fixed operation frequency. The performance of the antennas, in terms of reconfigurability, return loss and radiation efficiency, is promising for the development of fully-integrated graphene transceivers at THz.