If one has lost their passport and is in the process of getting a new one, do they lose their existing visa which was in their passport? Once they recieve the new passport and head to immigration do they get the existing time on their one year multiple entry re instated or are they asked to leave and re apply?

The current stay (90 days) will be transferred to the new passport. You have to apply for a new multiple entry visa outside Thailand.

When you visit Immigration you will be asked for port of entry, flight number etc, date and time of entry. You also need a letter from your embassy stating that your new passport is issued  for a lost one. Be sure you have these details, or even better, a copy of the relevant pages of the lost passport.

Thanks George appreciate the info. I have copies of last visa, front page old passport and the card from the airport.  I only had one more 3 month period left  on the one year anyway.

Thanks Again