Dipole moment of CH2Cl2 and CHCl3
As the dipolar moment is a vectorial property, you have to take into account both the number of chlorine atoms around the carbon atom, as well as their relative arrangement -- among them, as well in respect to the carbon atom.  

Lacking access to experimentally determined data about the molecular geometries,you may sketch the molecules in question, for example with Avogadro, and optimize the geometry (here, MMFF94 was deployed). You are literally able "to walk around" the molecule and its dipolar moment.



You easily will recognize a feature in common -- the similar direction of the resulting dipolar moment.  Simultaneously, you will recognize the different angle defined by Cl-C-Cl, too.  However, beside the angle, distances like C-Cl and C-H are affected by the different steric demand and electronic properties, too; equally influencing the overall dipole moment.  Hence the molecule of dichloromethane is more polar than the one of chloroform.

Sidenote: a force field like MMFF94 is a computationally cheap approach to optimize molecular structures.  There are better methods, but more costly; for the level of the question addressed, however, I thought it already provides the insight necessary here.