Hijack finds competitors by first locating the geo location or physical location of the business itself, then it does a proprietary search for other businesses starting at a 5 mile radius that we have social data for within the category of the business listing and or a few pre selected categories by the user. 
It's important to understand a few things as it relates to competitors, whom we show or list as a competitor may or may not be whom you expect to see as competitors for a few reasons, first the competitors and categories list are taken from our own list of businesses so we may not yet have all of the businesses that one might expect to see. 
Also we are constantly collecting new social data for new businesses and their user activity every day but we don't yet have all of the social data for all of the businesses on our platform like other social networks have so you may know or find a competitor say on Facebook that you know about for a particular client but does not appear on our competitor's list. 
There can be many reasons why the competitor you are looking for is not yet on our list, with 21 million businesses to process through we may not yet have found and mapped to that competitor's listing or we may know the competitor's Facebook or Instagram page but may not yet have sufficient user data to target that competitor's customers properly, it's important to note that, it's important to check back often to see if new competitors have emerged from our data set.
Even if we have that business listed we may not have any or enough social data for those competitor businesses to be able to put them on the list of competitors in a way that would benefit the system and or agency experience so we don't include them as competitors until enough data appears for those competitors for us to really use.

We shoot for a minimum of 30+ competitors for Hijack that the system tries to find so if it needs to it will increase that radius recursively (5 miles, then 10 miles, then 15 miles etc) all the way up to 100 or 200 miles in order to find potential competitors to pull data from, the reason for choosing to circle out to such a large radius of competitors is because we are ultimately targeting the users that have interacted with those competitors and may live within that radius and not necessarily the competitors themselves. 
Also some businesses might be listed under multiple categories, so a business that may not be known for pizzas but potentially serves pizza not as a primary but as simply part of their menu may be listed under pizza along with many other categories but the user interface is designed in such a way that if you don't feel that competitor fits what you are looking for then you are free to un check said competitor from your list. 
We also do our best to remove possible chains from our competitor lists as their social data potentially has people who are spread out all over the country, but if you see a chain you may feel free to remove it for better local accuracy, a lot of variables go into determining who should or shouldn't be listed as a competitor but as we collect more data you should eventually see the list get bigger and more refined as time moves on.