I am looking for my parents who live in spain?

My parents moved to Murcia in Spain, I have lost phone number, I have their address but it appears to be non excistant and mail returned, could be wrong address, need to know how to find them.

Some post offices here will not deliver mail if the post code is not correct, they even return mail to sender.
Simplest way without fuss is to put an ad in papers. There are several English language newspapers in the Region of Murcia. Just enter English language newspapers Spain in a search engine and see the list, contact them and put an ad in giving all details available, names where from etc. This could get a result as friends here of parents might see it even if parents do not.

You could also check to see if they have registered with nearest British Consulate, which is in Alicante, but then you run into difficulties due to privacy laws, etc.etc.

if they are residencia then contact the cop shop... of course you may have to speak the lingo... otherwise get a cheap flight and go and look...

Call a neighbor? One of their friends at home? ANother relative?

look for their telephone number in the white pages: www.paginasblancas.es

It may not be the wrong address. It could be correct but the postman doesn't know where it is. Believe me, the postal service can be good here but it can also be very bad. On top of that, many urbanisations or campo houses have no street names for the post office to go by. It may be you are not spelling their address correctly. It could make answering your question a little easier if you told us whether it was Murcia province or the city of Murcia.