The development of technologies at the terahertz frequency domain requires fast, sensitive THz detectors working at room temperature. Here we demonstrate a miniaturized resonator with a suspended beam that acts as a mechanical oscillator converting THz signals into mechanical oscillations at megahertz frequency. Thanks to the optimized thermomechanical effect on our resonators, they respond very strongly to the incident THz radiation with a responsivity of 4 nm/μW, and thus can be employed as sensitive THz detectors operating at room temperature. We further implement phase lock loop (PLL) measurements which show that the device can respond at high speed, on the order of 1 MHz, limited by the cut-off frequency of PLL. In addition to the terahertz detection, our system can also serve as a great platform for fundamental research when the mechanical oscillation is forced into a strong non-linear regime by an external drive. This effect can also be exploited to build reconfigurable logic gates for THz signal processing, which is studied in our ongoing work.