Informal:
* closer (Keep it simple!)
* closr (Shorten the word)
* cloz (Even shorter)
* cloze (Similar to "close" but with an extra letter)
* clsr (Another shortened form)
Formal:
* closer (This is the most accurate spelling)
Other Options:
* nearer (This word has a similar meaning to "closer")
* more near (This phrase is more descriptive)
Ultimately, the best way to spell "closer" for younger people depends on your audience and the tone you want to convey.