All what other people said, and yes, do check the rim and rim tape, and the end of the spokes (that could be poking through the tape). Punctures often come from the wheel itself.

Plus, there can be some grit or glass IN the tire that you don't see or even feel with your finger. Running an inflated balloon on both the inside and the outside of your tire, you'll probably find something (if all else fails).

Plus: to find the problem with a tube, inflate it and put it in water. See where the bubbles come from...