This question has a couple of dependencies, but it's very interesting nonetheless.
Firstly, it is essential to consider why this person has stayed inside this one circle. Secondly, it is important to consider the motivation for wanting to break out of this circle. Is it because of a desire to reach more ears? Is it because of a need to feel 'successful'? (the latter is often an important reason why new acts sign to majors, instead of smaller labels where they would have more freedom)
So the specific how / plan of action really depends on the style of music and personality of your friend. I see two roads:
- Expanding the circle. The least agressive way and most comfortable is to simply keep building. Ways in which this could be done is for instance by giving house concerts and doing gigs where people come in for free if they bring a member of the opposite sex (or if they're wearing matching hats, whatever) - the goal is to keep adding new people to the circle. Then you need to connect with those new people. Facebook and Twitter are a HUGE help with this; make sure to mention them at least 2 times when doing a gig; have them in the ID3 tags of digital audio; on all the artist pages; on physical copies, etc. This is a very personal route to take, so you have to connect quite intimately with fans (not literally, unless you're into that).
- The deep end. This is a different approach and it can be compared to 'cold calls' in sales. Basically, you're going for an audience that doesn't know you yet; at all. The biggest challenge seems to get your music heard / get discovered, but I think the real challenge lies in retention: keeping the attention of people who hear the music and "kind of" like it. Key to getting discovered is making / doing something worth talking about like Die Antwoord a few years ago or Fulkultur. This depends heavily on setting up social media monitors and Google Alerts so that you catch every single person who talks about you on the web, so that you can respond to them, connect with them and retain! That is just the first step; then it's a matter of utilizing the opportunities that arise.
Both ways are a lot of (very hard) work, but the latter is probably more intensive. Hope this helps and if you could provide more info, I'm willing to help/answer more.