COE necessary for working visa?

Is a Certificate of Eligibility necessary to get a working visa? If so, how can I get one? I don't know anybody in Japan.

Yes, I think it is necessary.

The sponsor of your visa will have to apply for the certificate of eligibility. In most cases, the sponsor is your future employer. In other words: you need a job offer to apply for most work visa types.

Uji is right. You cannot begin the working visa application process until you have a job lined up- it's not possible to get a visa and then look for a job I'm afraid.

If you have the funds to support yourself, you can come to Japan on a tourist visa and look for a job (although you must not tell Immigration on arrival that that is what you plan to do) and then change status to a working visa once you have found an employer to sponsor you.