I'm looking for a book series I owned a few books of in my childhood, they were compilation novels and I recall they had about three stories or so in each one. One of the stories I remember vividly was about a town where kids keep going missing (and ending up on milk cartons) and it's because of a blob that lives in the sewers. Unfortunately that's the only one I can recall off the top of my head but I remember another one of the books had a cover with an image of an evil looking dog that was black and red. I don't know if they came in paperback, but the only ones I had were all hardcover (if that helps at all)
Thank you for your help!