What you can do with a 24V supply is make a voltage divider with two equal value resistors to give a 12V point which then becomes your new virtual Gnd. The original Gnd terminal becomes your new '-12V' rail. However, if your circuit requires more than a few mA then the virtual ground would need buffering with a unity-gain amplifier (e.g. op-amp).
A resistive voltage divider would sort of work if the currents drawn from the positive half and the negative half stayed equal. Of course the resistive divider approach is inefficient in addition to being unstable. So it is a poor choice for most applications. In some applications there are other options, so can we have an explanation of the specific application, since there may be other options possible?