How to start a pencil portrait without using an outline of features?
I would begin by constructing the form and mass of the head, as often seen in figure drawing construction:



Images from Andrew Loomis's "Drawing the Head and Hands". Loomis is a very well-known figure artist and illustrator with a variety of instructional books that are very helpful.

This construction, in drawing from the mind, is usually done by understanding some sort of system of proportions and then altering features to add character. Proportions would compare head height to width, or divide head height into sections to place features (seen in the images above), but it can get much more complex.

By understanding these general relationships of constructing a figure, you begin to see how real heads and faces compare and vary. 

One popular method of achieving this development of form is called blocking-in. You can see a quality example of blocking-in using the Atelier method at GeorgetownAtelier.com. Depiction of bust of bare derriere in spoiler block, from that website.


   


You can start your base block-in similar to drawing an initial outline. But, instead of just focusing on the silhouette, think about the form in 3D. The outline will guide you on the proportions to use as you develop your other planes and shapes.

Then slowly add details, keeping your sketch light. You can measure placements of features, such as:


Where is the top arch of the eyebrow compare to the ears?
If you draw a straight vertical line on the side of the nostril wing, how far is the corner of the eye? (Or vice-versa)
Compared to the length of the nose, what's the distance between the tip of the nose to the bottom of the chin?
What degree of angle is it from the outside corner of the eye to the tip of the nose?
If you draw a straight vertical line on corner of the mouth, how does it compare to the center of the eye?


These are pretty limited examples. The key to getting an accurate portrait of a real person is by getting the proportions and placements correct for their anatomy. Since you can start with height or width, you can scale the other dimensions based on that, and then scale every other proportion on others you know you did "right".

The more you analyze the geometry, the more accurate you'll be. 

Measuring this way can be done with classical techniques such as using your pencil as a measuring stick, which can also be aided by a plumb line for getting objective verticals. Or, if you working from a 2D source, such as a photo, you can take accurate measurements of distances and angles using rulers and protractors.