You can't really achieve that appearance in Illustrator using 3D effects. Illustrator's 3D Extrude is pretty rudimentary and will never allow a flat front face with an extrusion. In order for any extrusion to show, using Illustrator's 3D effect, you must rotate the object. That's not what you have in your image.
What you can do to achieve this appearance in Illustrator is to set the front object, then copy it and offset it for the base of the shadow. Then manually add tangent objects to give the appearance of the shadow. In the example below the white S0 is the front object, the black So is the base for the shadow then the red shapes are all manually drawn tangent shapes.
When the red shapes are filled with black it gives the appearance of a block shadow as in your example.
Trying to do this with the 3D effect will simply be a lesson in frustration.
Another option is to use offset fills and stack them to create the appearance of the block shadow:
You simply add a fill in the appearance panel, then use Effect > Distort & Transform > Transform to move the fill away from the original object.
I've moved the black fill behind the contents of the object in the Appearance Panel. Then used Effect > Distort & Transform > Transform to move the black fill 1pt left and 1pt down. I've then inserted a number of copies. The depth of the block shadow will depend upon the copies. Since each copy is moved 1pt left and down, if you want a 50pt shadow enter 50 copies.
I use the Appearance panel technique most often. However in some cases, it can be much, much, faster and easier to simply draw tangent shapes depending upon the base artwork.