You can run Facebook ads that target the people who viewed the most pages of your website.
Technically, it's the people who fired the most PageView events. This event fires every time the pixel loads. That could be the same page or it could be multiple pages.
When creating a website custom audience, you would choose From Your Events within the Events dropdown and then select PageView.
Then, select "Refine By" and "Aggregated Value." By default, it will be "greater than or equal to" two.
This would then capture only those people who fired the PageView event two or more times during the past X days (30 days by default). You can change this however you want to isolate people who fired even more page view events if you want.
While this audience is bound to be small, it will also be your most engaged. You can use it for targeting to build your email list, sell product, or anything else. Know that volume is likely to be limited so you probably won't exit the learning phase, but these are some of the people who are most likely to act.
You can also use this as a source audience for Lookalikes. Just one more option for your targeting.
Try it out!
