Buzzer not buzzing in proteus 7.7v - used ic555
I have built this circuit in my version of Proteus, and your output of the 555 will only reach 5V output in this circuit. You can double check this by setting your scope to DC and looking at the output. This is likely due to the load the buzzer puts on the output.
Your buzzer is a 12V buzzer. Even if your output was equal to your input voltage of 9V, that's still not enough to drive the buzzer. When you are in the buzzer properties menu, change the operating voltage value to 5V and it'll work.
Alternatively, you could toggle an NMOSFET to switch the buzzer, and attach the gate to the output of the 555, but you need to ensure either a 12V supply, or change the buzzer operating voltage.
Both of these methods I have built myself and they work.