The only time you should need a spouse's social security number is if you are legally married and filing jointly (together) or separately (separated). If filing separately, your spouse's SSN is required so the IRS can match your returns and make sure you followed certain rules. If you don't have the SSN, you can't e-file. Print your return, sign, and file by mail. Attach a written statement explaining that you are still married but are out of touch with your spouse. Give your spouse's full name, birthdate, and last known address.
You may need to use a fake SSN to get Turbotax to allow you to print a return. Try 999-88-9999, then cover it with white-out before you mail in the return.
