Diversify growth streams.
Google will send you traffic, but Google can change quickly.
Get yourself featured more prominently on the company website, newsletters, or outbound emails to customers.
Get inbound links on major news sites which get lots of traffic.
Answer questions on Quora, Yahoo Answers, and Stack exchange.
Build up bases on social media that share the best content from the community.
Develop partnerships with major organizations to help drive traffic to the community.
Whatever you do, start looking at building new streams of members into the community.