Can hair grow through concealing fibers?

Hair grows from the root up and rarely do the follicles get "blocked." However, If you have a lot of fibers left on your scalp day after day and not washing them out, this may lead to an increase in the natural oils and seborrhea which is a scaly inflammatory condition of the scalp. Inflammation CAN impede hair growth. It's fine to use hair fibers, just wash them out regularly and keep your scalp clean and healthy. Also don't start using them too soon after a hair transplant as the fibers can irritate the new grafts and cause inflammation.

As long as you're using the Toppik properly (don't just overload your scalp with it) and washing it out on a regular basis, it shouldn't cause an issue with your hair growth. 

Dear Janemosk
As Jeff points out, there is no need for concern. Hair shafts will have no trouble working their way through Topik or similar fibres. Think of it as blades of grass working their way through soil.

No, camouflaging fibers do not block hair growth. You can use these without that concern. If you are using topical treatments, (such as minoxidil) these must be completely washed out before application of the minoxidil.

The answer to this question is generally Yes the hair can go through Toppik as mostly they just sit on the scalp.  What you want to be careful of though is using so much that they get into the hair follicles themselves and damage those.
Toppik in general should be usd sparingly, remember that even very healthy hair has some scalp visibility so don't completely cover your scalp.
Another option you might try while regrowing your hair is a henna scalp tattoo.  Remember the goal of Toppik is to reduce the contracts between the scalp and the hair so making hair thinness less apparent.
Don;t forget your ultimate goal however which should be to first stop and then reverse your hair loss and regrow your hair.
Look for a hair regrowth specialist who can identify and treat your personal root cause of hair loss and who offers a guarantee on results.

Yes, hair can grow when you have Toppik on it, but if you allow it to cake, it will grow under the 'cake'. Just wash it out regularly.