  In this work we extend the so--called Minimal Geometric Deformation method in
$2+1$ dimensional space--times with cosmological constant in order to deal with
the gravitational decoupling of two circularly symmetric sources. We find that,
even though the system here studied is lower dimensional and it includes the
cosmological constant, the conditions for gravitational decoupling of two
circularly symmetric sources coincides with those found in the $3+1$
dimensional case. We obtain that, under certain circumstances, the extended
gravitational decoupling leads to the decoupling of the sources involved in the
sense that both the isotropic and the anisotropic sector satisfy Einstein's
field equations and the final solution corresponds to a non-linear
superposition of two metric components. As particular examples, we implement
the method to generate an exterior charged BTZ solution starting from the BTZ
vacuum as the isotropic sector and new $2+1$ black hole solutions imposing a
barotropic equation of state for the anisotropic sector. We also show that the
imposition of a polytropic equation of state of the decoupler matter allows to
construct a regular black hole solution in three--dimensional gravity.
