Real Dictionary

come along
convention: You say 'come along' to someone to encourage them to hurry up, usually when you are rather annoyed with them.
phrasal verb: If something is coming along, it is developing or making progress.
phrasal verb: When something or someone comes along, they occur or arrive by chance.
phrasal verb: You tell someone to come along to encourage them in a friendly way to do something, especially to attend something.

come along in American English
to accompany someone, attend as part of a group
to appear or arrive

come along in British English
verb: to progress

come along! in British English
hurry up!