The buzzer probably needs a different signal than the light does. The audio buzzer has what they call specifications. These specs tell you what the buzzer needs to work.
The 555 has specs too...called a data sheet. This tells you what you can put in and what you can get out of the device.

This is why all the details are important. It's more complicated than building blocks.

Awesome tips BR-549, thank you. I just found this topic which discusses (in some part of it) the similar Buzzer waveform issues that I was wondering about:
http://mrobinson.org/blog/tag/toroid.html

Love you allaboutcircuits

 

If the buzzer is connected between the 555 output and ground (0 volts) try this:

-put a low-value resistor, anything in the range of about 30 to 60 ohms would be OK, between the negative side of the buzzer and ground - that is, in series with the buzzer lead
-set up your oscilloscope with the ground lead on the ground side of the resistor and the probe tip on the other end of the resistor
-run your circuit; adjust the vertical and horizontal of the oscilloscope to show us no more than about 3 or 4 cycles; there may not be much signal amplitude - if it is really low try a higher value resistor, such as 100-150 ohms
[EDIT - if the signal across the resistor is more than about 200 mV, try a lower resistance, as long as your scope can display the signal well]
-save a waveform and post it

Now be sure you have the 10 to 100 µF capacitor between V+ and ground, as Mr. Chips instructed. Also add a 0.1 µF (100 nF) ceramic capacitor on the shortest leads possible between pins 1 and 8 of the 555. Plug the leads into the breadboard in the holes right next to the 555 pins, and again - be sure the leads are as short as possible.
Show us the waveform, using the same oscilloscope settings as for the previous experiment.

What we are trying to do is measure the current into the buzzer and determine if good power supply decoupling (also called "bypassing") improves the waveform.

If you can please show us a picture of the buzzer.