Frank Ahearn strides up Third Avenue, New York, in his big suede boots, his thinning ponytail waving in the wind. He has a vente latte welded to his palm. Six feet tall, the goatee-bearded and denim-clad Frank M. Ahearn (pronounced Ayhern) could have walked straight out of a novel by his favourite mystery writer, Elmore Leonard. Like a Leonard character, he thinks fast and speaks faster. Born and bred in the Bronx – he now lives in Venice Beach, California – Ahearn notices everything that’s going on around him. Nothing escapes him, because Frank M. Ahearn is a skip tracer. One of the world’s best, he is employed by companies, private investigators and individuals to find people who have skipped town leaving behind debts, unpaid employees or angry partners.

“In 20 years, guess I must have found close on 40,000 people,” says Ahearn, ignoring a pedestrian stop light. “I’m a New Yorker, man, I want to get there today,” he shouts over the din of the traffic. “Most people who vanish just take off and go, right? BIG MISTAKE! I’ll find you,” Ahearn promises. “People leave behind their debts, they use their frequent-flyer programme to escape, not knowing that I can access that, along with their utility bills. People have no idea how many footprints they leave, how many connections they reveal.”

Creating a pretext or a scenario to wheedle information out of people and organisations is Ahearn’s key skip-tracing weapon. “You call up, you ask questions. In the end, every ‘No’ leads to a ‘Yes’,” he says, easing into a pizza at Grace’s Trattoria, an unremarkable Italian on East 71st Street. “I’m very persuasive on the phone, and the people who work those sites are trained to sell stuff, not protect information.”

The previous week in Los Angeles, it had been Ahearn’s turn to say “No”, to Sharon Stone and an offer to make a movie of his life. “I had dinner with her and her producers. They were not offering enough. Do they think I’m running a lemonade stall and desperate for cash?” Stone was interested, not only because Ahearn is a skip tracer extraordinaire, but because he has re-engineered his considerable skills to help honest people who have a genuine and compelling need not to get found by stalkers, kidnappers, violent partners or the Mob. Frank M. Ahearn is the man who can help you disappear.

As the world’s number one “privacy expert”, Ahearn is in such demand that his website, www.frankahearn.com (aka www.disappear.info), with its useful subsections entitled “Keys to Disappearing”, “Offshore Information”, etc, gets up to 90 hits a day. “For a lot of people, disappearing is just one of those ‘what-if’ fantasies, but out of those 90, around half a dozen will contact me seriously wanting advice on how to start over some place else.”

As the recession deepened, Ahearn began receiving so many e-mails from people who wanted to disappear, or insulate their dwindling assets, he has just published an 80-page guide called How to Disappear and Fall off the Grid... which can be downloaded for $19.99 (£14) from his website. “We’re selling around 40 a week, most of them to people who work in the finance sector or related industries in America, the UK, all over Europe and Russia.”

The skip-tracing side is also booming, with Ahearn’s business partner Eileen Horan shouldering a huge workload for finance companies chasing bad debts. In the past, these companies would have gone straight to the “repo man”, who would go round to repossess goods to the value of the debt. Now, Ahearn says, “They use us to identify where the hard assets really are before moving to repo.” The recession has been good to him.

One easy route to anonymity is to establish an International Business Corporation. IBCs, available in many countries, are both legal and allow for complete secrecy with directors and officers of the corporation not having to be listed. An IBC enables you to open an offshore bank account and get a so-called “black” credit card in its name, keeping your personal shopping history anonymous.

Surely this option is only open to the rich and financially literate? Not so, says Ahearn. “Anybody can set one up with, say, $5,000 [£3,500], and you can even do it online.” There are other ways to keep you off unwanted radar. For around $12 a month (£8), you can set up a JFAX or eFax account which means you can get a local phone number in almost any country. When someone calls that number, the message will be forwarded to your e-mail address. Nobody will know where you are. Use prepaid phones, internet cafés, and pay for flights in cash. “Anybody can do this,” Ahearn says. “I can make people hard to find, but fake identities I don’t do. They don’t work, and most times they are illegal.”

Neither will he help fake people’s deaths, a process known as “pseudocide”, much in the news since swindling canoeist John Darwin and his wife Anne were jailed last year for faking his death in a £250,000 life insurance fraud. “Having all those photographs taken of themselves in Panama was a pretty dumb thing to do,” Ahearn says dismissively. “After the Darwins were arrested, I got a lot of e-mails from people in the UK asking me to fix it for them to fake their death and disappear, but I’m just helping genuine folks get a little more privacy from those they don’t want to know, and to help them stay off the radar.”

Befitting a man who has the word “Freedom” tattooed across his back, Ahearn is always on the move, working out of a virtual office in California. He still flies weekly to New York, where his mum Ann runs a small business processing medical bills. His dad, also Frank, is seriously ill, meaning frequent bedside visits. Frank senior earned his living running illegal after-hours gambling clubs in the Bronx: “It was crazy, we even had a slot machine in the house where I grew up.”

Ahearn almost crossed to the other side, applying to join the NYPD when he was in his early twenties, but balked when he arrived to do the physical and saw all the men in uniform. Instead, Ahearn got a job working for an investigation agency in New Jersey that put undercover agents in shops to catch employees stealing. He noticed that a colleague, Scott, spent his time accessing vehicle records and phone bills to find people who had taken flight – he was a skip tracer.