I just downloaded the Visio Viewer and messed around a bit, but my guess is that you can't execute macros in it. It may be possible to recreate your search macro using the Viewer's object model, which basically just lets you iterate over all the shapes in a drawing by index, and you can pull out custom properties, so that may be enough for you to recreate your search macro.
Basically you'd want to have a function that looks for custom properties on a shape by name:
Function GetCustomPropertyVal(ShapeNum As Long, PropertyName As String) As String
Dim PropIdx As Long
For PropIdx = 1 To ctrViewer.CustomPropertyCount(ShapeNum)
If ctrViewer.CustomPropertyName(ShapeNum, PropIdx) Like PropertyName Then
GetCustomPropertyVal = ctrViewer.CustomPropertyValue(ShapeNum, PropIdx)
Exit Function
End If
Next PropIdx
End Function
so you'd just loop:
for i = 1 to ctrViewer.ShapeCount
if getcustompropertyval( i , "PropertyName" ) <> "" then
' Do something
endif
next i