"Tropa" is a relatively new informal term used to mean one's regular social group or gang. It's a term popular among Millennials, while "barkada" is how the older generations call their gang. "Grupo" is the general and more formal term for any group and "samahán" is the formal Tagalog term for an association.
"Katropa" = a member of one's gang
"May lakad ako kasama ang tropa" = I'm going somewhere with the gang. ("may lakad ako" is an idiomatic expression that literally translates to "I have a walk")
"Katropa n'yo ba si James?" = Is James a member of your gang?
"Tignán natin kung papayag ang tropa sa gusto mo." = Let's see if the gang will agree to what you want.
"Hindí kasí mahilig si Robert sa inuman kayá tumiwalág na lang siyá sa tropa" = Because Robert is not fond of drinking that's why he just disassociated himself from the gang. ["Tiwalág" = separated (possibly a maverick)]