For up to date information you should call the NADRA helpline (111-786-100)and explain your situation to them.
The process in my knowledge goes as follows:
1) You launch an FIR report with the Police about lost CNIC.
2) You take a copy of the FIR to NADRA office. They block your old CNIC and issue you a new one.
I've heard of people skipping the FIR, but you should ask the NADRA helpline to be sure.
For both of these you NEED your id-card number. Search your documents since you might have a photocopy lying around somewhere. B-forms have id card numbers as well if you have one, most legal documents (driving license, nikah nama, vehicle registry, property documents, sale\rent agreements etc.) mention id numbers, schools\employers usually keep a copy of your id as well. If you have any cell numbers in your name send 'MNP' via sms to 667 to get your id card number.
If all else fails NADRA may help you. NADRA supposedly has biometric matching and name search technologies, but I believe they don't use it in such situations. If your parents have computerised id NADRA can usually track you via their numbers. Otherwise there is a smaller chace of tracking your id via your siblings' id numbers (I've seen it fail). Your last chance would be a talk with some high up official or legal proceedings (court order where a judge declares you a citizen etc.)