Voltage regulator Current regulation
With any linear voltage regulator (current boosted or not current boosted) you are going to get this: -

Output current = Input current - a few mA to power the regulator

You are never (ever) going to see an output current greater than the input current. If you want that then you must consider a buck voltage regulator.


  So what is the impact of the PNP transistor in the circuit? How can I
  boost the current in my circuit? If I want to see 5W output across my
  load(53.33ohm in the schematic) what are the changes I should make in
  the circuit?


If you want 53.33 ohms to dissipate 5 watts then the voltage needed is governed by the formula: -

Power = \$V^2\div R\$ or

Voltage = \$\sqrt{P\cdot R}\$ = 16.329 volts


  I tried to simulate the same circuit but with input of 12V, 0.1A and
  7805 regulator


The 7805 produces 5V on its output and not 16.329 volts.