Can we use Stop Words while using multinomial navies theorem?
The basic task here I get is sentiment analysis of tweets. So for this, we can first extract features and then use a classifier. Stop words are those which are present for grammatical purposes but do not add any value/meaning to the sentence.
So, yes you can remove the stop words from the tweet, extract the features and then pass it to the classifier. You can get already existing stop words from

from nltk.corpus import stopwords
stop_words = stopwords.words('english')


Removing the stop words doesn't always improve the accuracy. 
Take a look at this as it is a very similar problem statement as yours. Hope it helps!