There are a couple of strategies to locate the missing junction.
The first step, with the power on, is to map out, as best you can, the routing of the wires. This can give you an idea as to how the place was wired in the first place.
Next, take a good look at the place, and try to guess what changes have been made over the years. Have outlets been added? Walls moved? Is one part newer than another?
Finally, with the power off, use a "data" toner to attempt to map out the dead outlets.
Now, let's assume that you decide that the break has to be between two particular outlets. The first thing you do, using your toner from both ends of the "broken" wire, is to double-check for any lights, switches, or junctions between the two points. If so, check those places next; if not, then it is usually best to abandon the old wire and fish in a new one.
When you abandon a wire, it is usually best to avoid damaging it,or cutting it back. Why? Because you are sure to get another call in a few months, complaining that something isn't working- and that "something" usually turns out to be something you disconnected when you abandoned the wire- and may even have been the cause of the problem in the first place!
This is also a good time to document what you have learned about the house- you'll appreciate it later!