Fans went online to mourn the loss of musician Michael Jackson, posting tributes on Twitter and on the Michael Jackson website. Major search engines Google and Yahoo shared traffic trends on Friday, with Google reporting one of the largest mobile-search spikes ever.

But fans weren't just searching, listening to music and leaving tributes online - they were also scouring websites for memorabilia. About.com's collectibles guru Barbara Crews wrote that Michael Jackson's passing was probably the biggest celebrity death since the Internet has grown and matured to the point it is today. "Collectors know that anytime someone famous passes away or there is a newsworthy event, great interest is shown in memorabilia of the person involved."

Just how much is Michael Jackson memorabilia worth? Authentic items have doubled in value, according to appraiser Gary Sohmers, who appears regularly on the PBS television program Antiques Roadshow and is known as the King of Pop Culture. But Sohmers warned that most of the Michel Jackson items available for sale on the Internet are probably fake.

Joe Orlando, President PSA/DNA Authentication Services (a division of Collectors Universe) cautioned that Michael Jackson usually didn't offer fans frequent autograph access. He said in a statement that autograph buyers may not have adequate consumer protection even if the signature is accompanied by what appears to be a certificate of authenticity.

Smart Money magazine published an article on Friday titled, "Should You Invest in Michael Jackson?" with advice on what, and when, to buy and sell.

There are great differences in just how much an item is worth, depending on the nature of the item. The Seattle Post-Intelligencer blog spoke to Golden Oldies music-store owner Dean Silverstone who said that while some unopened copies of the album "Thriller" were going for $1,200, he won't sell them for more than $5. They'll never be worth more than $10 because there were so many of them, he explained.

eBay and Amazon capitalized on the demand for Michael Jackson-related items by putting messaging on their home pages with links to product pages.

eBay was affected by Michael Jackson's recent death beyond the interest in the pop star's memorabilia - people used eBay to buy and sell tickets to Jackson's planned summer concerts in England. eBay UK placed a ban on tickets for Michael Jackson concerts on Friday, including a ban on tickets listed as memorabilia. It also announced it would ensure that all buyers on the site could receive a full refund for their ticket purchase and that it would refund eBay's sales commissions to sellers when they refund buyers for Michael Jackson ticket sales.