Vw2017 can also import OBJ files which typically include material and texture files, so that will give you another option for finding 3D people to import.
Also don't forget SketchUp and the 3dWarehouse.
When your imported DWG or DXF files import as white or grey it means that they do not have any associated materials or textures. DXF as a file format is quite outdated and does not support material definitions, so I would not bother looking for a 3D person in DXF format. For the best direct importing into Vw, I would look for 3DS, OBJ or SKP formats.