I found it!
Grahame Baker-Smith, Jo-Jo's Journey (Bodley Head, 1994).
Forced to crash land his space ship on Earth, Jo-Jo the interplanetary collector gets into one scrape after another with his new friend Daisy.
There are a few copies floating around the web (AbeBooks, Amazon, Ebay). The blurb reads:
Interplanetary collector, Jo-Jo, is being pursued by the dark ships of an enemy planet. Forced to crash land, he heads for the nearest habitable planet — the Blue Planet — known to its residents as … Earth! From here in it's non-stop adventure for Jo-Jo and his new-found earth companion, Daisy. Jo-Jo's troublesome pet, Meep, is never far from his side as the three friends get in and out of one scrape after another. But when Jo-Jo decides to add a dinosaur skeleton to his collection, Daisy knows that this space boy needs to be taught a lesson …
This stunning graphic novel has an action-packed storyline and exquisite illustrations. Space Boy, Jo-Jo, and punchy heroine, Daisy, are ideal characters to entice children into the world of children's books.
My original post:
I'm almost certain I read the same book in the late-'90s or early 2000s. Unfortunately I don't have it anymore (it was probably donated to somewhere) and haven't been able to find much information online. The name of the alien boy was definitely Jojo (or Jo Jo/Joejoe/Joe Joe, et cetera).
Everything mentioned I recall being in the book. There are a couple of other things that I remember. The alien boy had blonde hair that curled under his eyes and formed points. When his pet, the fox-like thing, drank the milk the young girl put out for her cat, the creature turned a different colour. The girl and her mother lived in a tower block/apartment building that may have been in New York. There was also a feast where the creepy alien lady ate space bugs.
I read it in English too and it was a paperback. Colour. Somewhat unique style, and relatively lifelike. It seemed to be a standalone story.