As other answers already say, hanging out sounds less childish than play.
There's a slight difference in meaning, though, too.
The word play often connotes playing around with some toy or game: playing marbles, playing with dolls, playing with Legos, etc.
The term hang out refers to spending time together, but not necessarily doing anything in particular: hanging out at the mall, hanging out after school.
When kids are hanging out, they are probably just standing and talking – usually at some location away from home. If they are playing, then that gets associated with playing some game or sport.
Another key is that play sounds childish by itself. Much like in the movie, a teenager is susceptible to being mocked if he says, "Anybody wanna play?" However, that same teen could probably get away with something like, "Anybody wanna play basketball?"
Words I learnt today.
Words I have learnt today.
Words I learned today.
The words learnt and learned are the past tenses and past participles of the verb learn. Learnt is chiefly used in BE.
The sentence #1 is in the past simple; it talks of today that is over.
On the other hand, the sentence #2 is in the present perfect; it also talks of today but it's not yet over. It's still daytime. Of course, you still have some time to learn more words.
Best Answer
I would say "Please add me as a Snapchat friend." Another option that is very slightly awkward might be "Could you add me as a Snapchat friend?". "Could you" is maybe a little more formal which is a tiny bit odd in this context. "Add me up" would be used more like a situation where you are closing out a bar tab at a bar and you ask the bartender to "Add me up" meaning "add up my bill so I can pay."