I work in advertising, and have dealt a lot with copyright issues, and regularly discuss such issues with dedicated copyright lawyers. The bottom line is, if you make a face that looks like a celebrity without their permission, you're in trouble; they could sue you, even if the product was free and your intentions were good. The problem lies in the fact there is no control over the usage of the freebie; people could use them to create artwork that was considered detrimental or damaging to the image or career of the celebrity. As the creator, you could be held legally responsible. There is a possible way round it, and that lies in the definition of the term "inspired by". It is better if you make a face that is not exactly like a celebrity. You can be inspired by a celebrity, but if you add a mole, or change the nose slightly etc, you could be OK. And never call your created face by the same name; even if it doesn't look exactly like them, if it has the same name as the celebrity then it is clear that it was your intent to reproduce their image, and they could even sue you for not getting their face right, which lawyers could argue was damaging to their client in itself! However, if it doesn't look exactly like them, and you don't use their name, then there really isn't much point in doing it, is there?
My advice is; don't do it at all. You can easily make thousands of beautiful faces that don't look like celebrities, so why give yourself extra hassle?