Pimp Your Sound allows you to create ringtones from the tracks on your device.
However, in order to be able to add track to the app you need to be sure that the track is saved directly on the device, not in the cloud.
If you have iTunes match activated on your device - make sure that the track is still saved on the device.
When you make a ringtone out of a long song - please remember that tunes longer than 30 seconds can be used as Ringtones only. Please choose shorter sounds for Text Tones, Mail and Tweet Tones, Calendar and Reminder Alerts.
If you still have questions - reach us at firstname.lastname@example.org!