Push-pull Amplifier Class AB
Its not the biasing - in fact there is no problem.
That circuit is not a voltage amplifier, its a current amplifier - the key feature being that both of your transistors are configured as emitter-followers (gain ~ 1).

What you have there is a common configuration for the output stage of an audio amplifier because it can drive lots of current into your speaker.

You need to add a voltage gain stage in front of it in order to amplify your 100mV signal into something that the output stage can use.
The easiest way is to cheat and use an opamp...