If you're reporting your net worth to somebody (like a bank), then you would report it at whatever value it reasonably has in the current year. Unless you have some notice that it's a failing business, that would normally be what you invested in it (or, if you've received purchase offers - you can use that to value it).
For your own calculations/financial planning - that's up to you. My experience with personally having this kind of investment is that even if you expect it to make money, you cannot know when or how much. In the calculations I do with my own financial planning, I value speculative investments as 0, unless they are currently producing income.
This is a conservative approach - you basically value it as a total loss until it's not a total loss. But I've had business partners who planned around companies being worth X, only to experience distress when it was a loss.