The 35 to 54 year old age group, a sweet spot for law firms seeking to build relationships with clients, prospective clients, and referral sources, is the leading age group for mobile social networking via Facebook and Twitter. This per a report from Marketing Charts on the exploding growth of mobile Facebook and Twitter.

Despite the stereotype of teens spending every waking moment on a mobile device, Nielsen data suggests their parents actually spend more time performing mobile web surfing. Only 7% of mobile social networking activity was represented by 13-to-17-year-olds and only 16% by 18-to-24-year-olds in December 2009.

The leaders in mobile social networking activity are 35-to-54-year-olds, who accounted for 36% of mobile social network usage in December 2009. Close behind them were 25-to-34-year-olds, who performed 34% of the month’s mobile social networking activity. Users ages 55 and up combined for the remaining 7%.

The overall growth in the mobile use of Twitter and Facebook last year was staggering.

Access to Facebook via mobile browser grew 112% in the past year, while mobile Twitter access experienced a 347% jump, according to a new study from comScore.

In January 2010, 25.1 million mobile users accessed Facebook via their mobile browser, up 112% from 11.8 million mobile users in January 2009. While only 4.7 million mobile users accessed Twitter from their mobile browser in January 2010, this represented 347% growth from 1.05 million mobile users in January 2009.

Building relationships by engaging your target audience is the essence of client development for you as a lawyer or law firm. Client development success for law firms is not all about websites, search engine optimization (SEO), and pushing out digital alerts and newsletters by email. It’s about listening to your clients, prospective clients, referral sources, and the influencers of those three. And then engaging them. The result is relationships and legal work.

In order to listen and engage your target audience as a lawyer or law firm, you need to go out to where your audience is. Today your audience is increasingly at Facebook, Twitter, and other social networking sites. It behooves you to start learning how to engage your target audience at these places.