Playing games such as Farmville or poker via social networking sites has become commonplace. Bingo Friendzy is likely to be followed by other gambling games. I was one of many who voiced concerns when it launched. My main concern was that the game features cartoon characters similar to Moshi Monsters (a favourite of my youngest son). I don't believe gambling games should feature anything that might encourage children or adolescents to gamble. Although players have to be 18 to play Bingo Friendzy, research has shown that adolescents bypass minimum age limits for Facebook by giving false information.

Many games played on social networking sites have gambling elements. Even if money is not involved, they introduce children to the principles of gambling. Research shows that players can become excited even if playing with virtual money. Social networking sites have the potential to normalise gambling behaviours. Teenagers are learning the mechanics of gambling.

Other research has demonstrated that one of the risk factors for problem gambling among adolescents was "play for free" games on the internet.

Observers have accused companies such as Zynga of exploiting psychological principles to bring in new players from a demographic who may never have played games before.

However, that alone does not explain the success of Zynga games. Other features, such as appealing characters and graphics, and (what some might deem) aggressive viral marketing tactics, also appear to play a part.

The introduction of in-game virtual goods and accessories (that people pay real money for) was a psychological masterstroke. In this sense, it becomes more akin to gambling, as social gamers know that they are spending money as they play with little or no financial return. The question I am constantly asked is why people pay real money for virtual items in games like Farmville. I have studied slot-machine players for over 25 years, and the similarities are striking.

Many hard-core slots players know they will lose every penny – they are playing with money rather than for it. To me, this appears to be what social gamers do too. Like slots players, they love the game itself. So, allowing those who play social games the chance to get their money back (or more) is why companies operating social games want to get into pure gambling. This extra dimension to social games could be a huge revenue generator.

Dr Mark D Griffiths is professor of gambling studies and director of the International Gaming Research Unit, Nottingham Trent University