What is my 401k balance

You have no idea? Who holds your 401K? You should have received a statement from them as a fiduciary. Do you contribute?

How would you expect a site like this to know? You should have been getting regular statements. If you haven't contact the company where the 401(k) was administered.

If people on a public site knew what you had in your 401K and where... You should be very concerned about that.