Genymotion Desktop does not support virtual webcams, such as CamTwist, Virtual Webcam or akvcam. It is also not possible to loop or fake a webcam. Only physical devices are supported.
For your webcam to work properly with Genymotion Desktop, it must support the UVC standard (USB video device class).
Here is a list of webcams supporting the standard: http://www.ideasonboard.org/uvc/
This is the reference list regardless of your environment (Windows, macOS, Linux).