Develop an AC - equivalent circuit
Hybrid-pi model of the transistor (for low frequencies) is this:


Now let's fit the block in the circuit:







simulate this circuit &ndash; Schematic created using CircuitLab

$$
r_\pi = \frac{V_T} {I_{B(DC)}} = \frac{\beta_{DC}} {g_m} \\
g_m = \frac{1}{r_e} \text{; } r_e = \frac{V_T}{I_{C(DC)}} \Rightarrow g_m = \frac{I_{C(DC)}}{V_T} \text{  ;} V_T\text {: Thermal voltage}\cong 26mV \text{ @ 24°C} \\
r_o = \frac{V_A + V_{CE}}{I_C} \cong \frac{V_A}{I_{C(DC)}} \text{; }V_A: \text{Early Voltage}
$$

Now you can calculate the gain \$ K_v \$ from \$ \frac{Vo}{Vin} \$.