It is probably an issue with your web3 version. I guess you installed web3 v1.0. As of web3.js v1.0, you have to go through
eth in order to reach personal from nodejs.
NOTE : You may not find many tutorials to start with web3 version 1.0 since it is not that stable, yet.
Go to migrations folder and edit
1_initial_migration.jsfile by replacing
web3.personal.unlockAccount(web3.eth.accounts, "passphrase"); with following line:-
This should help, else I would recommend using version email@example.com
PS: I am using firstname.lastname@example.org