When looking for missing people, the first thing that you should consider is the circumstance of their absence. Did they leave on their own volition? Do you know of any reason for their leaving? Is there risk or threat on their life that is connected to their disappearance?
Having weighed these considerations, try to locate them immediately. Call their families, relatives, close friends and anyone whom you know have some connection with them one way or the other. Also try to get access with places you know they usually visit such as salons, barbershops, dental clinics, auto shops or any place where they habitually hang out.
If there is no clue as to where they could be found, and you believe there is risk or threat on the life of the missing person, it is time to inform the police. Report the incident to the police station nearest you. Make it a point to provide all details possible such as: the place and time they were last seen; the clothes they were wearing; the people they were with and other related information. The police will then take the next steps to track down the missing person.
If the missing person is still not found despite police assistance, it's time you resort to other means. Run a publication in newspapers in the Missing Persons section. Issue radio and television releases in your area or the place where the person was last seen. You may employ the assistance of government agencies. Ask your local post office if there is any mail that has been sent to the person concerned that has been forwarded to another mailing address. Or better yet, send a letter to the last known address of the missing person. If the mail is returned to you, chances are, the postmaster general has written a notification on the envelope that can give you a significant clue.
Write the Clerk Court in the area of last residence of the missing person and ask if there are any cases handled by the court that could have involved them. You may also check with local agencies such as the city records office, city assessor's office, business license office, voters' registrar office and the department of motor vehicles. These agencies can give you important information on the probable activities engaged in by the missing person thus giving you a hint on where they can be located.
To make your search truly exhaustive, make sure not to leave any stone unturned. One very effective way of tracking people nowadays is through the Internet. Even if the missing people are not Internet users (particularly older persons) you'll never know the possibility.
There are some Internet sites that offer assistance in locating people. Visit these sites, sign up and see what information you can get. You can also try to look in blogs and social networks for whatever clues that can guide you.
Side note: Finding missing people can entail some expenses on your part such as travel and communication costs and certain fees required by government agencies for giving you assistance in locating records pertinent to your search.