This paper presents design and numerical investigations of an ultra-compact, and highly-efficient plasmonic absorber based on metal–insulator–metal waveguides. The proposed device offers multiple narrow-band absorption at visible and near-infrared wavelengths with peak absorbance between 81 and 100%. The finite element method has been used to simulate the proposed structure. The simulation results show that the resonance wavelengths can be easily modulated by tuning the coupling distances between the input and output ports and the triangular resonators. To find the optimized size of the proposed structure, maximize its efficiency, and attain narrow-band resonances, a parameterized genetic algorithm has been used. Taking into account the obtained notable specifications of the proposed structure, it can contribute to the development of miniaturized and efficient optical components for photonic integrated circuits.