You should seek the advice of counsel immediately. There are services that attempt to track and trace assets.
You should also become acquainted with your estate. You should make copies of all relevant documents regarding assets. You should hire competent counsel in an effort to trace assets.
Generally speaking, it is very difficult to hide assets. The hiding of assets is a violation of a fiduciary duty that binds both spouses during the marriage.
In addition, because the Preliminary Declaration of Disclosure requires the spouse to list and disclose under penalty of perjury, the existence of all assets, the spouse hiding the assets runs the risk of significant civil liability and even criminal liability, should they elect to hide assets.