Go to https://www.facebook.com/ (desktop) or tap the Facebook app icon (mobile). This will open your News Feed if you're logged into Facebook.  If you aren't logged into Facebook on desktop, first enter your Facebook email address and password in the upper-right side of the page, then click Log In. On mobile, you can log into Facebook by entering your email address and password when prompted and then tapping Log In. Click or tap the text box near the top of the News Feed page. This text box usually has a phrase such as "What's on your mind?" in it. This might be a joke, a fact, or a general statement, but stay away from topics that will evoke strong emotions in your friend group.  Avoid mentioning sensitive or partisan issues. Don't tag anyone in your status, as doing so will skew the test results. It's in the bottom-right corner of the status window. On mobile, you'll tap Share in the upper-right corner instead. After a certain amount of time (e.g., 8 hours), review the status to see who liked it. If applicable, make a note of who commented on the status as well. You'll want at least 5 different statuses to compare against each other. If you noticed that a large number of the same people liked and/or commented on your Facebook statuses each time, they're probably visiting your Facebook page more often than other people in your friends list.

Summary:
Open Facebook. Select the status text box. Type in a neutral status. Click Post. Wait to see who likes the status. Repeat this test several more times. Compare the mutual people who liked your statuses.