Hi there!
I haven't read any of the other responses to your question, so I'm not sure if you've found assistance already---if so, disregard my ramblings! I am a special education teacher, working with three to five year olds who have disabilities. In am NOT inferring that your child has a disability BY ANY MEANS, don't stress! I just thought I'd offer a bit of advice. My thoughts are also in regards to older toddlers (three to five years), not infants, as it is completely normal for infants to chew and suck on everything they come in contact with. Your child's chewing habit is hopefully a phase that will be short lived.
Your intervention should, of course, always be based on your child's abilities and needs. Always begin with the least intervention that you find effective. If simple reminders do the trick (without creating other adverse behaviors) then that is the best way to go.
A step up from that could be for you to have crunchy/chewy HEALTHY snacks readily available. When you first notice the "chewing" behavior, offer your child a carrot, celery, or pretzel, etc., and tell them to ask for one of these items instead of chewing/sucking on inappropriate items. Make your explanations and examples as literal as possible while keeping them as short as possible too.
Small children need lots of LITERAL explanations. We often assume they understand all vocabulary when they don't. For example, you may need to explain what "chewing" is. If they don't understand the main words in a direction, they can't possibly follow the direction.
If you need a more intensive intervention, then your goal is to "redirect" the behavior toward a more appropriate outlet. What I would recommend is giving him something that is readily available to chew on. Something attached to the body helps prevent thumb sucking or ruining clothing. We use a plastic tubing at school (like 1/4" or 1/2" thick). You can tie it into a necklace or bracelet. We also use wet washcloths to satisfy the chewing need.
Thumb sucking and pacifier use is detrimental to speech and language development. Not only is it harmful to the development of their gums and teeth, but children who always have something in their mouths don't get in enough "talking" practice and revert to grunting, pointing, and gesturing for things rather than verbalizing.
Good luck! I hope that was helpful in some way.