Head shots are always fairly popular and you can use all kinds of sources for them such as stock photography or tools such as Poser (found on the Smith Micro site) and Adobe Mixmo / Fuse as well as Daz Studio (there are others such as tools from Reallusion Character creator / iClone and Makehuman.org) or of course, you can get images via your own camera of friends, models, of just selfies. Pity that PS has no in built feature but with the tools mentioned, a ready source of resources are available to create all kinds of vector face shapes.
Personally, I generally create most of my heads in Poser but the new Mixmo tool is pretty good, Daz Studio is also a good alternative (and is free). Of course, you are limited to the heads that you have with the app or ones you have purchased but the tool does offer a vast range of ways of creating all kinds of expressions, facial looks, emotions, speech and more. To actually generate the head, the 3D model must be rendered and these can be rendered in numerous ways such as sketch rendering or using the new render tool, Superfly. If you decide to use photos then you will need a really good nice clean photo of the head to be used in any creation of a vector shape. Take the photo or rendered file and import it into Illustrator (or Corel Trace)
If you are using Photoshop as part of the creative cloud then you will have Illustrator as well and you can import the artwork in Illustrator via the place command or open command. Once you have the raster image in AI, you can then select and then go to the top of the app and select the image trace option. Open the image trace panel (also along the top option bar) and set the mode to black and white and set the threshold / paths etc to as required (more or less black and white) and set the ignore white checkbox to ON. And then click expand (again, along the top option bar). Go to the object menu and select the ungroup command and then do a little tidying up as there may be a few extraneous paths such as white (which shouldn't be there but sometimes still turn up) and remove all those paths other than the black (use the select menu to select similar paths such as same fill and stroke). Once you have a nice clean path, select all of them and then use the pathfinder panel (found via the window menu) and combine / unite. Copy path. You can also create many variants of this using perhaps different effects such as poster edges added to the artwork in AI (or before) to create a nice edge for the image trace to use and perhaps combine that with adjustments (in PS or AI) such as using the edit menu edit colors and adjust balance and grayscale to turn the image into a much stronger black / white image (with only the black lines if you wish to create a more illustration look) but you can use all kinds of other plugins such as edge effects found in the Photoshop Plugin Collection
On paste, select the custom shape option and then go to the define custom shape command in the edit menu to add the face to the panel - there you have it, a lovely head image for use in PS. Not sure of any particular plugin or tool to do this in PS though so a combination of AI and PS is probably the best way to go.