If you believe you may have filed with TurboTax, you can try our account recovery process - https://myturbotax.intuit.com/account-recovery/.
To check if you have more than one User ID, go to the Account Recovery page, enter your email, and we'll provide you a list of logins tied to that email address. If you have more than 1 email address, you should run the tool on each one.
NOTE: If you are logged into a TurboTax account, sign out first (including this forum), then close the browser and reopen it. Then go the account recovery tool via the link above.
If you don't find it with that method, then run the tool again, but this time, use the small blue link that says "I don't know my email address or User ID", and it will look up at your accounts by your SSN and other parameters.
If you aren't able to find it using this way you can always contact the IRS to see if you filed - https://www.irs.gov/help-resources/telephone-assistance