Who's using sequelize?
... we are avid users of sequelize (and have been for the past 18 months) (Feb 2017)
We've been using sequelize since we started in the beginning of 2015. We use it for our graphql servers (in connection with graphql-sequelize), and for all our background workers.
We have used Sequelize in enterprise projects for some of our Fortune 100 and Fortune 500 clients. It is used in deployments that are depended on by hundreds of millions of devices every year.