Millennials are already a force to be reckoned with in the marketplace, and their buying power will keep growing for the next few decades to come.

Also known as Generation Y, they are the set of individuals who were born in the United States between 1980 and 2000, some 79 million strong, making them the largest generation ever in terms of numbers. By 2020, millennials will be involved in 30 percent of all retail purchases and comprise 50 percent of the workforce.

Even now, with many millennials still in school, they wield considerable economic influence, with about $170 billion in buying power a year, as ComScore estimated in a 2012 white paper. Brand marketers who hope to succeed as millennials transform the marketplace in coming years need to learn how to engage them as customers. Here are some insights: 

Related: Millennials Check Their Phones 43 Times a Day. This Is What They're Looking For. (Infographic)

1. Millennials don’t trust online advertising. As members of group that grew up in times of turmoil, millennials tend to distrust institutions, including corporations. Just 6 percent of the millennials who participated in a 2013 survey by my company, Social Chorus, said they find online advertisements credible. So if online advertising is a mainstay of your company's marketing strategy, you may want to reconsider your approach so as to reach this audience.

2. They share experiences online. As digital natives who have been wired practically since they were in diapers, millennials are typically on social media constantly and feel driven to share experiences with their friends in real time. Make sure they are having positive experiences with your company's brand to share.

Related: Millennials Spend 18 Hours a Day Consuming Media -- And It's Mostly Content Created By Peers

3. Millennials trust their friends. Ninety-one percent of millennials surveyed by SocialChorus said they would consider buying a product if a friend recommended it. This illustrates golden opportunity for companies to market with millennials rather than to them. If you can get millennials to serve as advocates, you’ll drive reach, awareness, engagement and sales. To achieve this, companies should develop a brand-advocacy strategy. The first step is to identify potential brand advocates such as social media followers, employees and topical bloggers. The next steps are to give them incentives to share the brand story and measure the impact.  

4. Gen Yers use social media-based feedback. User-generated content is a primary source of information for millennial customers who are considering a purchase. To maximize your company's return on investment, make sure you provide an easy way for customers to share their thoughts about your product and services and provide feedback.

5. Millennials like to share entertaining content. One of the best ways to get millennials involved with your company's is to provide valuable, entertaining content that they will want to share with their friends on social- media platforms. Keep that goal in mind when developing marketing campaigns.

6. Gen Yers are a socially conscious group. Although they’ve been unfairly portrayed as self-absorbed, millennials are a very philanthropic group, and they look for social responsibility in the companies they do business with. Make sure your brand conveys a socially responsible image.

7. Millennials value openness and transparency. Perhaps because they were raised during tumultuous times, Millennials tend to be suspicious of companies’ motives unless they are reassured by an open and transparent approach. Gain their trust, and you’ll capture their business.

Engage in two-way conversations with millennials on social media platforms like Facebook and Twitter. Share company news on social platforms. Let customers know their voices are heard by responding promptly to the feedback you receive. If you gain millennials’ trust, you’ll capture their business.

Related: Millennial Misconceptions: How You're Totally Wrong About This Generation