Formal:
* Sama ka sa pagsigaw. (This is the most literal translation, but it sounds a bit formal and can be used in a general context.)
* Ayalo ka sa pagsigaw. (This is a more polite way of saying "join me" and is appropriate for most situations.)
Informal:
* Sama-sama kita magsigaw. (This emphasizes the togetherness of the action and is more informal.)
* Sigaw kita dungan. (This means "we'll shout together" and is a more casual way of saying it.)
Depending on the context, you could also use phrases like:
* Ipagsigaw mo ako. (Shout for me.)
* Magsigaw kita para... (Let's shout for/against...)
The best translation for you will depend on your specific situation and the tone you want to convey.