Never say "wanna"!  You will immediately sound non-native, or like someone with very poor English. No-one will think you are serious.

The phrase "join with" suggests "connect". This is not the same as becoming part of a group. "Join in" means participate. This is also different from "join".

You should say to the manager, "I would like to join your company."

 I am a native speaker from Texas in the USA

If you want someone to do something with you you would say  "Do you want to do something with me?" or be specific "Do you want to get coffee?"  You don't need to really say "with me."   You would never say "join with me." If you said "join me in a game of chess" it would be fine but it would be better to say "Do you want to play chess."

If you want to work somewhere you would say "I would like to work for your company" (you wouldn't say join the company).  Never say "join with"  in any case.

Hi there,

 The only time I've heard the phrase "join with me" used is in public speaking events where the speaker invites the group to "join with me in singing" or "joining with me in congratulating..." (applause would follow).

1. When I want someone to do something with me, I say: Join me. 

But is it ok if I say : "Join with me!"?

2. If I want to work for a company, should I talk to the manager: "I wanna join your company" or "I wanna join in your company" or "I wanna join with your company?" 

Thanks so much! 

1. "Join with me" doesn't really work. You could say "come with me" or "You should join me" (I'd use "You should join me" or "you should come with me", since it's less of a command)

2. You should say "I want to join your company" or "I would like to work for your company", the other two examples don't need the with or in

I hope this helps!

Hi, I'm Elizabeth, a native English speaker from Houston, Texas.

A few things have come up in this discussion.

1. Do not say "join with me". I don't think I've ever heard anyone say that. You can definitely say "join me", or, int he case above, "I want to join your company". As you can see, the preposition "with" is incorrect. When you use "join", it is followed by a NOUN (person/place/thing). For instance, you say "join ME" or "join YOUR COMPANY". 

2. As for the "wanna" thing, I say "wanna" all the time. But if you're applying for a job, DON'T. "Wanna" should be used casually and with friends only. I personally don't WRITE "wanna", I only say it, but I don't consider it a huge red flag if you do write "wanna" like that when texting a friend. But NEVER for anything formal. 

3. You can absolutely say "May I join you", because it is followed by the noun "you". Therefore, it is grammatically correct. I hear that phrase all the time. But if you say "I would like to have your company", it IS grammatically correct, though I don't think it means what you think it does. "I would like to have your company" means "I want to POSSESS your company" or, in a command, "give me your company". It does not mean you want to join the company, it means you want to OWN the company. 

I hope this helps.