100% agreement with Devin. Beyond that, be careful not to treat Circles as a social network simulator. Its real job is to determine whether characters are friends or enemies.
Circling up someone you already know and who is established in the story is perfectly valid. Afterall, they're already known and established the second or third time you make a Circles roll to bring them in.
In your case, if and when you do decide to ask for a Circles test to meet with the gang boss, what the test will actually be doing is determining how the boss feels about the character. Does he consider him a son? A friend? A valued lieutenant? A dangerous upstart who will soon outgrow his usefulness? Does he think the character is a snitch? Has he simply decided to sacrifice the character like a pawn in pursuit of some goal?
A Circles roll will determine whether it goes one way or the other, and then you'll decide what that means, maybe using one of the examples above or something completely different.
I corner him and stab him in the face!