The default scaling of IMVU’s underlying system is extremely large so assets loaded in for editing in Maya tend to extend outside the cameras normal viewing range giving the impression that nothing has opened or imported into a scene. Thankfully this can be addressed without changing or rescaling the assets, which should be avoided, by adjusting Camera Attributes and Working Units.
When initially loaded into Maya absent a Workspace profile, IMVU’s assets clip outside the viewports field of view so can appear as though nothing has loaded. This can fixed by setting the Far Clip Plane and Near Clip Plane attributes of the viewport camera in Camera Attributes. Once an IMVU Starter File has been opened or imported, from the View menu  click Select Camera  – View » Select Camera. The entity will highlighted in the Attribute Editor. Expand the Camera Attributes section and check or change Near Clip Plane to 1 (Near Clip Plane: 1.000), and Far Clip Plane to 10,000 (Far Clip Plane: 10000.000) . This sets the cameras clip plane so the IMVU meshes should be visible.
Design note: for most avatar based content Far Clip Plane will typically need to be 5,000 or above, 10,000+ for large furniture items and rooms.
The fix for this is to first adjust the ‘clip’ values for the views camera, increasing it to accommodate the large scaling IMVU uses – from View  select the camera  then alter its attributes, checking or changing Far Clip Plane  with an appropriately large value.
After setting camera clipping, if the IMVU assets are still not visible, next set the Working Units of measurement in Maya’s Preferences. From the main Windows menu  click Settings/Preferences then on Preferences  – Windows » Settings/Preferences » Preferences. In the dialogue that appears, find Settings  then in Working Units change the Linear setting to meter  (Linear: meter).
If the IMVU assets are still not visible in the Poly Modeling viewport double-check the user zoom level, i.e. how close the camera is to scene centre by zooming out or using View » Frame All.