Having exhausted your own searches online and with friends, it may be wise to engage with a professional investigator; one that is proficient in the arts associated with finding people swiftly and in a focused manner. If you are sincerely concerned for their wellbeing (in terms of mental/emotional health) or if you think they are in danger of harming others or themselves, it may be worthwhile approaching the police. However, if this is not an option or is in any way inappropriate or the police are unable or unwilling to help, it could be worthwhile speaking with an appropriate investigator.