Get some tape and lay it over the area and push it down. If glass is there, it will stick to the tape. Its kinda like the way you run tape over clothes to get rid of lint.

That is a great answer!

Misjudging the distance I had in my room, I knocked over a glass with the headstock on my guitar. I picked up a few large pieces, and I think I got all of it, but I can't be sure. I would just vacuum it up, but my vacuum broke a few days ago. Is there any way I can tell if there are tiny shards laying on my floor?