It seems to me when police say this it's a (excuse the phrase) cop out of searching for them. It typically requires no evidence of motive for foul play, when they see no reason for suspicion they will say that it was probably voluntary so they don't have to search any longer (that and they have probably run out of leads themselves). Basically they are just saying they will no longer actively search for the person. It doesn't really mean that there is a zero percent change that there was no foul play or that they have evidence that they had voluntarily gone missing. It's just there is a lack of evidence that they were taken against their will.
If the person has fled voluntarily it would be nice of them to tell someone, however doing so is dangerous to that person being harassed by the people that want them found. It's important for their friends and family to remain vigilant in case a lead does turn up.
http://www.missingpersonsofamerica.com/2011/05/when-adult-is-voluntarily-missing...
It seems to me when police say this it's a (excuse the phrase) cop out of searching for them. It typically requires no evidence of motive for foul play, when they see no reason for suspicion they will say that it was probably voluntary so they don't have to search any longer (that and they have probably run out of leads themselves). Basically they are just saying they will no longer actively search for the person. It doesn't really mean that there is a zero percent change that there was no foul play or that they have evidence that they had voluntarily gone missing. It's just there is a lack of evidence that they were taken against their will.
If the person has fled voluntarily it would be nice of them to tell someone, however doing so is dangerous to that person being harassed by the people that want them found. It's important for their friends and family to remain vigilant in case a lead does turn up.