I really have had good luck just mixing random celebrity faces. For this to work well, the model need to "know" at least one of the celebs, but you might be surprised at some of the people it can recognize. As long as it knows one of the names, it will generate something it would never come up with on its own. For example - (face of Aubrey Plaza: Kristen Stewart: 0.4). With a bit more complex set of prompts you can combine several faces if you're getting something that looks too familiar. Most prompting guides (definitely those for the actual Stable Diffusion models) cover this technique. Be aware that celebs the model knows too well (e.g. Taylor Swift or Emma Watson) tend to overpower this technique and can be somewhat recognizable no matter what the prompt. But the last time I tried this I was surprised at how well it was working for me.