We have developed an evolutionary algorithm (EA) for the global minimum search of molecular clusters. The EA is able to discover all the putative global minima of water clusters up to (H₂O)₂₀ and benzene clusters up to (C₆H₆)₃₀. Then, the EA was applied to search for the global minima structures of (C₆H₆)_n⁺ with n = 2−20, some of which were theoretically studied for the first time. Our results for n = 2−6 are consistent with previous theoretical work that uses a similar interaction potential. Excluding the very symmetric global minimum structure for n = 9, the growth pattern of (C₆H₆)_n⁺ with n ≥ 7 involves the (C₆H₆)₂⁺ dimer motif, which is placed off-center in the cluster. Such observation indicates that potentials commonly used in the literature for (C₆H₆)_n⁺ cannot reproduce the icosahedral-type packing suggested by the available experimental data.