Up to 25,000 people a year in the U.K. are illegally promoting financial products or offering financial advice on social media, but none have yet appeared in court, according to the first Treasury Select Committee meeting on the subject of so-called “finfluencers.” Regulated financial services firms must comply with strict guidelines when they promote their products on social media and may be put at risk by unauthorised finfluencers.

Ruth Prickett graduated from Cambridge University with a BA hons in History and has specialized in business and finance journalism for the past 20 years. She was editor of Financial Management, the magazine...