Using S-parameters of the transistor, it is only possible so simulate small signal/linear behaviour of the amplifier. For example linear gain. To simulate non-linear properties, such as RF output power, 1 dB compression point, OIP3, etc a non-linear (SPICE) model of the transistor is required in the simulations.
Contact the transistor manufacturer for availability of a SPICE model of the transistor. In most cases it's available upon request, even if it's not presented in the data sheet or on the web.