Your best bet if you haven't done it already is to log in through whatever online system is offered by your 401(k) provider. If you haven't done it already you'll need to have your social security number handy (and possibly your account number). If you can't get online, contact benefits or HR and ask for the 401(k) providers 1-800 number. Last resort would be a quarterly statement, but if you have moved and not updated your address, it's possibly your statements aren't being forwarded to your new address which is why the 1-800 number is your best bet.
Hi there thanks for reaching out. You need to contact the human resources department of your current or former employer or the investment provider of the 401(k) plan. Do you still receive statements or know how to contacts these entities?