In the US, we use "hey girl" a lot when we're chatting with our friends. Depending on how close of a relationship you have with the person you are talking to, it is acceptable to just say "hey" or "good morning" without really addressing the person. For me, it is acceptable to begin a conversation without a greeting when it is someone that I have a close relationship with. Let me know if you need help or have any questions!

I don't like to say hello or hi to my friends, I usually go straight to the point, I don't know whether it is ok or not

You could use: Hi bud / buddy [informal],

Hey gf (girlfriend) / girl, [informal].

Hello my friend [more formal]

or combinations of the above.

Every time I start an informal conversation with friend on whats app or texting.I feel confusion about words to initiate healthy interaction.

Thank you! (-: