Lovepaki

First thing your friend needs to do is inform the US embassy that he has lost the passport with the visa on it. Thereafter request for another visa appointment. It may be up to CO to grant that. If granted, your friend needs to pay the visa fee. They may want to see a good documentation including police report of the lost passport.

We are all.in.the same situation we have been under ready for interview since February 17.. when we emailed about that ready for interview issue we was told my fiance is under AP.. no details will be given. But make sure you keep track of the updates date changes i was told 8 update without any emails send means is closer for your approval visa.
Keep us all.in your prayers. Amen!