Access my wallet using a 16 digit passphrase
Unfortunately, that 16-digit passphrase is likely the password to decrypt your bitcoin core wallet.dat file. So you'll need to have that file in order to access your wallet.

It could also be a BIP-38 protected paper wallet, but it doesn't sound like you have one of those. 

Your best bet may be to search every email inbox, dropbox account, backup hard drive, or whatever else you may have, for either a backup of your wallet.dat file, or evidence of an account with an online wallet service.