Oh...actually. Being a former staff of a 'successful-ish' game, we focused more on "keeping regular visitors coming back" rather than focusing solely on bringing new faces into the community. The logical explanation of why these two approaches vary are as follows:
Regular visitors already have built an 'image' of the game, community and its staff. It can be a negative one but usually this is not the case. The pressure usually lies on the staff members to act as role-models (though I'm pretty sure everyone knows this); after all, people come for the game but stay for the community. If members have a positive view of staff, they will begin to feel safe and valued which in turn will help them build a a positive opinion of how things are run (on top of game quality and interaction, though that's not so important if you think about it), then they will keep returning and with a bit of luck they will start voicing the positivity that lies within the community.
On top of staff being friendly, understanding and non-judgemental (and flexible when it comes to punishment, 'cause people can and do change so second chances are a good way to rebuild what was lost); there are also other key factors in helping a community grow and prosper.
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1. Holding regular events (in-game and forum)
I think this is one of the more important ones. It's a way of getting a large portion of the community to engage together with staff - after all we're here because we share an interest (a.k.a the game) so it's great when members can start enjoying an event meant to bring people closer together - MOTS is actually a great example of that.
2. Building a true image of staff
'Staff are still people, just with responsibilities of maintaining a friendly environment etc.' - When members see staff joking around, participating in member-run events, and acting like 'any well-behaved member would' the members begin to feel closer, more connected. As stated before, staff are the prime representation of any community. And their approach impacts more than meets the eye.
3. Encouraging creativity
As with any community, there are bound to be very talented and creative users. Encouraging them to share their art, or perhaps them creating small 'OC gifts/drawings' can actually affect the member in many ways. One being that they begin to feel like their talents are not dismissed and/or they begin to discover new ones (which is great, and they'll always refer to the person or community that had helped them discover their newly found passion). Gifts of OC's (more so art of 'friendship groups' and such) can build a stronger bond between already existing members. I mean, come on - if you are having a wild time with your friends in a community and then are gifted an art containing your friends, or particular individuals that have made a huge impact on you (positively), you'd be floored wouldn't you. The whole concept of group drawings are too adorable aaaa! - I swear I've seen either a staffer or member with a group drawing and I felt my heart melt because it showed such 'togetherness'.
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Coming back to the more-regularly applied approach of focusing just on bringing new members into the community. If you just focus on raising the amount of users in a community, things will eventually crash and burn. You see, a community exists and is kept stable by old and new members alike; old members share amazing/not so amazing memories and stories and can impact the views of a new member, who in turn can start running around spreading positive or negative views which were acquired from regulars. Lacking old members would actually impact a community big time as new members would feel a little lost or confused not having a 'full picture' of a community and how it is run.
Anyway, I think I'll stop babbling because I intended on just giving a few points here and there and ended up expanding on each a little too much. So, I'll actually leave it up to you guys to refer back to this particular comment of mine or apply those points to your own community - after all it's worth giving a shot in my opinion. Have fun and feel free to expand or discuss the content of this post (or feel free to skim over it/ignore it i don't mind).
Have a nice day,
Wai wai.