Clicking on, off court

With a championship-caliber squad on the floor, the team is stepping up its digital game for devotees who can’t get enough of Pierce, KG, Rondo, and Ray on television and can’t score tickets to TD Garden.

The team recently began distributing exclusive locker room footage on YouTube, and last week launched 3-Point Play, an interactive stats prediction game for fans on the Celtics’ Facebook page. The Celtics are also sending Twitter messages, including quotes from press conferences and team events, to 21,000 followers and using the social networking site to offer seating upgrades at games.

These efforts augment GameTime Live, an application available at Celtics.com that features real time scores, tweets, and blogging with supporters throughout the world. The team beta-tested GameTime Live during the 2009 postseason, and more than 50,000 unique visitors checked it out during the triple-overtime loss to the Chicago Bulls in Game 6 of the first round.

“Now that we’re at this sold-out state, it’s more difficult to get into the game and fans can’t get tickets,’’ said Rich Gotham, the team’s president. “We want to make sure we don’t forget about those fans. We want to keep them interested and keep them loyal.’’

Basketball buffs are demanding deeper interaction, or a “second screen’’ experience, as Gotham calls it. While fans watch the game on television, many are also tweeting and surfing the Internet - traffic on Celtics.com spikes 100 percent during games. The National Basketball Association is rolling out a centralized version of the Celtics’ GameTime Live as a way for other teams to connect with supporters online.

“With sold-out games, we have 18,624 people in the building. But we could have over 20,000 online at Celtics.com,’’ said Shawn Sullivan, chief marketing officer for the Celtics. “It’s almost like there is a whole other game going on.’’

Sports marketers say it makes sense for a team to capitalize on the fan frenzy on and off the court and groom younger enthusiasts. Other local pro teams, including the Bruins and Red Sox, also have a presence on social networking websites. The New England Patriots, on Twitter for the first time this season, have nearly 30,000 followers who receive injury updates, game notes, and photos.

The Celtics, with 445,000 fans, are the second most popular NBA team on Facebook, behind the Los Angeles Lakers. In coming weeks, the Celtics are planning to launch Club Green Kids, a children’s club that will rely largely on e-mail and online efforts to communicate with members.

“The Celtics have a very affluent, techno-savvy fan base. They would be crazy not to do this as it reinforces their hipness as a sports franchise to their older fans,’’ said Chris Cakebread, a Boston University professor who teaches advertising and sports marketing. “And this clearly helps reach their younger fans, who, the Celtics hope, will one day be wealthy and can afford to become season ticket-holders.’’

Making Celtics.com a destination also helps the team’s bottom line. Sponsors are increasingly looking for ways to connect digitally with fans, and they are willing to pay more money to partner with the Celtics if millions of supporters are visiting the team’s website and the Celtics can e-mail or tweet promotions to fans worldwide. The team is also hoping to stream games live by early next year and create other mobile applications.

Although Celtics officials are eager to fuel the fandom now, the online outreach is also meant to help the team when times aren’t so good. By creating a database of fans, along with their preferences, the Celtics will be in a good position to tailor promotions and find Celtics buffs wherever they are.

“The last thing we want to do is sit on our hands,’’ Gotham said. “Our popularity has reached an all-time high, and we want to take advantage of the opportunity to build a bigger fan base so that during leaner times that will pay us back.’’

Jenn Abelson can be reached at abelson@globe.com.