I've had a couple normally law abiding friends get arrested on warrants that they've had for years without knowing. It would be a traffic ticket from long ago that they either forgot about or their was a mix up in payment. Given time that ticket slowly turns into a warrant and eventually an embarrassing arrest.

A friend from Texas discovered this whilst on a road trip, when he arrived at the Canadian border. He had to turn around and drive home, because of an bounced cheque from ~a year beforehand - that he'd never heard anything about since paying it.

The implication being that the police aren't doing a very good job of contacting people about warrants. The first they're hearing about it is by seeing themselves on Pinterest. Imagine the number of increased arrests if the police started using email.

Its rather different, but we are doing a load of outpatient healthcare work for an overworked public health board. Often calling patients multiple times over several days (on cell phone and landline) produces no contact with the person we are after. Posting a letter asking them to call us nearly always works. It's a slow process, but even when you know where someone lives, getting hold if them is hard.

Exactly; the whole reason they're on this site is that the police can't find them. It's reasonable to believe a decent percentage of them would have no idea that they're wanted.