So how do you find someone you have lost touch with? There are many ways to answer this question because the simple truth is it really depends on what you are looking for that person for as to how you go about finding them. For example, if you want to find someone you went to school with you could try Facebook to locate them, you just open a free account and then search for them using the simple search options, most people under 50 years old (and many over) use Facebook on a very regular basis so this is a great starting point.
Facebook took a lot of business of Friends Reunited in the UK but it is still worth having a look on Friends Reunited to see if there is any match for your old school friends. If you are looking for a recently moved tenant who owes you money or someone else who would prefer to stay under the radar you may find the simplest solution is to use a tenant trace service, it is quicker, more accurate and most operate on a no find no fee basis. If you are interested, take a look at How to Find Someone.
If you need an address finde service to locate someone's address who has moved, may be to send a Christmas card or birthday card this uses the electoral roll to search for people's current address.
If you are looking to find someone you have never seen such as a relative you didn't know you had or a school friend who isn't on Facebook or Friends Reunited you could try to find that person using old records from a site such as ancestory.co.u k which allows you to access birth and marriage records or even the nation archives file that has lots of information regarding various aspects of time gone by.
How to find someone is a good question, there is a large amount of trial and error involved, try different sites and see what they offer.