Feedback Circuit schematic to Control Theory block diagram?
In principle, you have nothing to do than to convert known formulas (relationships) into corresponding blocks.

Here is a basic example how to draw a closed-loop block diagram for the feedback effect caused by the emitter resistor Re in the classical BJT amplifier stage:

vbe=vb-ve with ve=ieRe and ie=ge*vbe (emitter related transconductance ge=Ie/Vt)

Hence, the input summing block makes (vb-ve) and the output (vbe) enters the closed loop consisting of the block [ge] and the block [Re]. 

Comment 1: In control theory it is common that blocks do not change units (amplifiers, controllers, attenuators,...). However, this is not a requirement. In the above example, we have a unit change from voltage to current and then from current back to voltage.

Comment 2: The above example shows that such a construction of a block diagram gives a visualization of a feedback loop - even if such a loop cannot be identified in the circuit diagram.