In Social Media when does interest become obsession and obsession become stalking?

[REIBroker]

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When it comes to the point of photographing a person for a 'sale' (which fall into printed social media, via: People, Star, and Sun Magazines) and it interferes with their freedom as an individual, thus causing fear of their personal safety, harm, and or death, as in the cases of: Princess Diana, Britney Spears, and Sienna Miller.

Taking photos at EXTREME distances, thus reporting in the media the person's personal actions that were supposed to be private: Prince William playing ball the day before the wedding

Chat rooms of stars that are willing to share some of their personal information and a viewer/active participant takes it to the level of showing up at the star's home: Jodie Foster, Mel Gibson

Because of news articles of their starring in films or TV roles: Rebecca Schaeffer was shot and killed, when a fan dug her name out of the DMV records.

Madonna, Michael J. Fox, and Scott Bakula have all faced crazed fans. Fans that have crossed the line and taken interest in seeing their stars in magazines and on the television and moved it into the real world, forcing the stars into a confrontation, by envading their homes.

Sources have been listed in the answer, except for abclocal.go.com