The author of Poet X is Elizabeth Acevedo, and as someone else mentioned she has published two other books.
My 13 year old was quite slow to read for fun but then got hooked on series, though he hasn't read much at all in the last few months. He started reading Lord of the Rings and has got completely stuck and not picked it up for a few weeks - hasn't even been taking it out of his school bag. I had to go into my local library before lockdown to sort out some of my books as they keep threatening to charge fines again (though not for school age kids, which is better, and reservations are also free for kids and teens even in normal times, though I need to ask whether it would be free for us to reserve suitable books from grown up shelves for him to read on his card).
He devoured a lot of thrillers by Charlie Higson, Malorie Blackman's 5 Noughts and Crosses novels, and some of the same author's other books, Cressida Cowell's two series, Philip Pullman's Dark Materials trilogy and his Book of Dust - 2 books so far, 2nd ends on a really outrageous cliffhanger which personally I'm really upset by (and I only heard parts of the very abridged radio adaptabion). DS1 liked the Mortal Engines books and another series by the same author, Philip Reeve. Also two series from Ali Sparkes.
At 14, he will probably be having to read books for adults, some with quite adult themes, etc at school. They actually read The Hunger Games in English lessons and for homework, which I would say perhaps 14 up and parents being aware that the trilogy has some dark stuff in it, late in year 7 or early in year 8, and he devoured the other two.
At the moment, many libraries are running limited opening hours/browsing access/service and some are closed, but if and when they are open, many public library services are offering to choose readers a bundle of books they might like. Or you can get him registered at some point and borrow some choices for him, then if he bites you can buy him more books.