If you've already tried locating your father through friends and family, the next place to turn is the internet. With more than 2 billion users, the big dog in this hunt is definitely Facebook, but other social media apps can be useful.

Begin by entering your father's name directly into your browser's search bar. This will probably yield an unusable, large number of results, most of them wildly unrelated to anyone who could possibly be your father – searches for public figures often yield more than a million results. But you never know, particularly if the combination of your father's first name and last name is unusual. Another possibility is to include a middle name, which will narrow results considerably.

If this doesn't work, try Facebook.

What makes Facebook so important when you're searching for a lost father is its large user base, which continues to grow rapidly, with more than 2 billion active users in 2017, up from 1.5 billion two years earlier. An active user signs into the app at least once a month.

If you haven't already signed up as a Facebook user, you'll need to do that first. Go to facebook.com/reg and follow a few simple instructions. The whole process takes about two minutes, after which you're signed in and free to use the site.

If you're using a smartphone, once you've signed up Facebook the first time, it will appear as an app on your phone. Thereafter, to get onto the site, simply click on the app. On a computer, the process is very much the same, although you'll need to type "facebook" in the browser's search bar to begin.

Once you're on Facebook, type your father's name into the Facebook search bar. If you get an unreasonably large number of returns, narrow the search in one of several ways (and you can also try combining two or more of them):

• Add his middle name.
  
• Add his place of birth.
• Add the last city he lived in before he disappeared.
• Add your mother's name: "John Doe May Doe."
• Include a hobby, profession, sport or social interest: "bowling," "accountant," "baseball" or "line dancing."
• Add "death": This isn't the return you want to come up, but sooner or later it happens. Don't immediately panic if you get a positive return; there'll usually be plenty of death notices with the same name, none of them necessarily your father's.

Every name that comes up in a Facebook search has either a photograph of that person or of something they'd like you to see (cute animals) or a somewhat ghostly generic avatar. To the right of the photo or image you'll see an "Add Friend" box. Clicking on it sends a friend request. Be aware that many Facebook users won't respond to a request from someone they don't know, but since this is your father, he should recognize your name.

If a person you've friended turns out not to be your father, you'll both start getting lot of daily updates and information that neither of you particularly wants to see. The polite thing to do is to prepare a short note of explanation that you can paste into the message box with the comment that you'll now unfriend them. Unfriending is as simple as friending. Go to that person's profile; then to the Friends list at the top and click "Unfriend."

YourFamily.com is a social media site dedicated to locating lost family members. FamilySearch, another good family search site, is run by the Church of Jesus Christ of Latter-Day Saints and has a large and growing database.

Existing database searches on both sites are free. Each site searches a variety of public records, such as birth records, death and marriage notices and events covered by media. This approach differs from Facebook's, which, although it has the largest database, searches only for Facebook users.