4,000 yuan of gold jewelry, friends took it to say that they were lost, can they sue him for fraud, there is no evidence,

Can't.
but he can sue him to embezzle the crime.
The crime of embezzlement refers to the fact that the property, forgotten or buried objects that are kept by others for illegal possession are illegally occupied by themselves. The subject of this crime is the general subject. Natural per capita of criminal responsibility capabilities at the age of 16 can constitute the crime. In terms of subjectively, this crime must be intentional, that is, knowing that it belongs to the property, forgotten or buried objects that other people keeps with themselves, and still illegally occupy it.

The Article 270 of the Criminal Law stipulates: "The property and objects of others will be illegally occupied by themselves, and the amount is large and refused to be refunded. Or fines; if there is a huge amount or other serious circumstances, it will be imprisoned for two years and less than five years, and a fine. " The second paragraph of this article also stipulates: "If the forgotten or burying objects of others illegally occupy it, the amount is large, and if it refuses to hand in, it is punished in accordance with the provisions of the previous paragraph."

That's not a friend