The charity has warned that the elderly and those struggling the most are facing an "invasion" through their computers, phones, letterboxes and on the doorstep from fraudsters.
Citizens Advice said up to four million people could be scammed each year as many incidents went unreported.
A study found a third of scams (34%) were over the phone, a quarter (24%) were through visits to a website, 16% were via letter or fax and 10% were through emails.
Counterfeit cashier cheques, fraudulent lenders offering loans to get hold of personal details, dating scams, ticket cons and computer hacking were among the most commonly reported examples.
Online shopping and auction fraud was the biggest single type, with almost 40,000 recorded cases.
Citizens Advice, Citizens Advice Scotland and the Trading Standards Institute have launched Scams Awareness Month and are urging people to "fight back" against fraudsters. Citizens Advice Scotland said it had seen a 14% jump in the number of bogus selling scams in the past year, but believed that to be only the "tip of the iceberg".
Daniel Gray, from Citizens Advice Scotland's Community Action Team, said: "Scams take on all sorts of forms, and con artists can find you online, through the post, over the telephone and even on your doorstep.
"One of the reasons scams are so common is because people don't report them. Research has shown that, while half of us have experienced some kind of scam, only 5% of us report it. That's shocking and if we give scammers that sort of free ride, it's no wonder they keep on going."