If you backup with iTunes and you restored from the backup and the contacts were gone, then there is no where to retrieve them from unless you have another backup that contains those contacts.
Launch iTunes on the computer and go to iTunes>Preferences>Devices. You will see a window with all of your backups listed in it.
If you see a recent backup that you are certain contains the contacts that you need, recover deleted contacts from iPhone.
If your contacts is gone from iCloud.com there is only a few ways to possibly recover it.
The first things I would check is a iCloud Backup, a iTunes Backup, or a 3rd party email that may have contained the contacts. To restore from a iCloud or iTunes backup follow this link. This article explains how to restore a device from either back up.
Note if you have backed up since the contacts went missing, you will not have the note on the backup. Make sure you do not back up if trying to restore from a back up as this will back up the content without the note.
To get to the "Set up assistant" on an iOS device, you must go to Settings>General>Reset>Erase All Content and Settings. Once the phone restarts, you will be at the "Set up Assistant"
Since you have previous iTunes backup, you can easily extract the contacts from the iTunes backup by using an iPhone backup extractor. After saving the found contacts to PC, you can import them to your Google contacts or iCloud directly.
In addition, there are also other ways to recover deleted iPhone contacts:
- Scan iPhone with a third party recovery software;
- Copy from old phone’s SIM card;
- Sync with Google contacts or other cloud service.