This paper deals with the eigenvalues extraction and steady-state forced vibration response of single-layered graphene sheets (SLGSs) with and without atomic vacancy defect using atomistic finite element method. The multi-body interatomic Tersoff-Brenner potential is used to represent the energy between two adjacent carbon atoms. Based on the Tersoff-Brenner potential, a new set of force constant parameters is established for graphene sheet, and the equivalent geometric and elastic properties of the space frame element to represent carbon-carbon bond are derived which are consistent with the material constitutive relations. Different values of aspect ratio and contours of SLGS are considered along with clamped, bridged, and cantilevered boundary conditions. A computational sine sweep test is carried out on the atomic structure of SLGSs with and without atomic vacancy defect within the frequency range of 0 to 10 THz. The vibration characteristics of SLGSs are also investigated under an impulse excitation. The response of SLGSs to the harmonic and impulse load over an applied frequency range is calculated. The response of SLGSs with an atomic vacancy defect is also compared with that of without defect to study its effect on the vibration characteristics. The results have been validated using molecular dynamics simulation and with those available in the literature.