In the manga, Mob's focus is mainly on his psychic abilities and personal growth rather than having a romantic relationship. So, no girlfriend for him.
In some comic storylines, Loki does have a girlfriend. But it depends on the specific comic run and version of the character. Sometimes these relationships are short-lived or complex.
Luffy is still alive and kicking in the manga. The story keeps evolving with him at the center of the action, encountering new enemies and growing stronger.
Well, you could start by joining clubs or activities you enjoy. That way, you'll meet girls with similar interests. Also, be confident but not cocky, and always be a good listener.