Some points to consider:
1. Are you syncing contacts with any other service, such as an email address (like gmail or yahoo, etc) or with Facebook, etc.? If so, these contacts likely still exist with those services, and they are just not streaming to your device at the moment. If this is the case, it is a simple fix usually to get them streaming properly again.
2. Are you logged in to the right user account on the computer? I can't tell you the number of times I've worked with people claiming the same as you and it turns out they were logged into the wrong user account on the computer, and their data was still safe and resting in THEIR account, waiting to be manipulated.
3. Syncing contacts and other data does not happen WITH iTunes, but rather THROUGH iTunes. If you were indeed syncing contacts and other info data classes through iTunes to you computer, that data may still be extant and accessible through their respective programs. On PC, iTunes will sync contacts, in particular, to most modern versions of Microsoft Outlook, Windows Contacts, or, with XP, Address Book. On the OS X side, contacts would have been synced with "Contacts" (Mountain Lion) or "Address Book" (Lion, Snow Leopard, Leopard, etc.)
4. If you information has EVER been synced with anything else outside of what has been mentioned above, there is a chance we may be able to recover the data partially. Think for a little while, and see if you can ever remember a time when you may have added your contact information to anything else, computer-wise, internet-wise, etc. and if you come up with ANYTHING, no matter how remote, please let me know, as it may hold a key to resolving this issue.
Please tell me more about your situation, including the items requested above. Also, if you have not yet, I recommend checking your phone for evidence of iCloud integration by going to Settings>iCloud. If you are logged in to iCloud, it should present you with a list of info items that can be synced with an ON/OFF switch next to each one. Otherwise, it will ask you to log in.
Any and all data you can provide me about this situation would be of great help in assisting you with resolving this issue.