c9012 PNP Transistor Equivalent

No you cannot use BC557 in place of C9012. 

The collector current of C9012 is 500mA whereas for BC557 it is only 100mA. So if your load is consuming anywhere more than 100mA it will damage the transistor permanently.

So you can try with BC527 or 2N5401 Transistors. They have the same pinout and the characteristics are more or less similar. 

Do keep in mind that these are just suggestions it is not possible to suggest a perfect alternative without knowing about the circuit where it will be used.

It is completely depends upon your application. If you are simply doing hobby project with a normal 9v battery then you can use any general PNP transistor, but if  your circuit is doing some practical job, then you cant replace C9012 with BC557 because of low current rating of BC557.

Please mention your uses and if possible share the image of circuit diagram.