Beginning on January 1, 2011 it became illegal in California for anyone to impersonate someone else online.
According to Senate Bill 1411, it is now illegal to “knowingly and without consent credibly impersonate another actual person through or on an Internet Web site… for purposes of harming, intimidating, threatening, or defrauding another person.”
Here is the law:
(a) Notwithstanding any other provision of law, any person who knowingly and without consent credibly impersonates another actual person through or on an Internet Web site or by other electronic means for purposes of harming, intimidating, threatening, or defrauding another person is guilty of a public offense punishable pursuant to subdivision (d).
(b) For purposes of this section, an impersonation is credible if another person would reasonably believe, or did reasonably believe, that the defendant was or is the person who was impersonated.
(c) For purposes of this section, “electronic means” shall include opening an e-mail account or an account or profile on a social networking Internet Web site in another person’s name.
(d) A violation of subdivision (a) is punishable by a fine not exceeding one thousand dollars ($1,000), or by imprisonment in a county jail not exceeding one year, or by both that fine and
(e) In addition to any other civil remedy available, a person who suffers damage or loss by reason of a violation of subdivision (a) may bring a civil action against the violator for compensatory damages and injunctive relief or other equitable relief pursuant to paragraphs (1), (2), (4), and (5) of subdivision (e) and subdivision
(f) This section shall not preclude prosecution under any other law.
This would apply to setting up a Facebook or Twitter account purporting to be another person, email accounts, or blogs or websites.