I'm finishing up a book called "Creative Play Therapy with Adolescents and Adults: Moving from Helping to Healing." It's going to the publisher this week and should be released in 2020.
I incorporate expressive arts through the child centered play therapy lens, and it works really well. It's especially helpful when wrapping words around an experience is difficult, such as trauma or complex emotions. The expressive arts are the "toys" and don't feel juvenile.