"When did they last check-in?" The YOTREPS Tracker page helps answer this frequent question but please remember that even in the normal course of events marine communications can be very difficult to maintain. If you do not find the boat you are looking for listed here, under NO circumstances is this sufficient to conclude that they are in any difficulties.
The reports data base is built from largely unchecked raw data. Many reports are passed over HF radio as voice transmissions and particularly when radio conditions are poor, it inevitable that errors will occur. Please be tolerant.