FRANKFURT (Reuters) - One of Germany's longest-running business court cases reopened on Thursday, with the lawyer for the plaintiffs against Deutsche Telekom <DTEGn.DE> urging judges to speed up proceedings as his clients were getting too old to see the results.

"Plaintiffs are dying on us," lawyer Andreas Tilp told the higher regional court in Frankfurt, which has been told by Germany's supreme court to determine damages in the case first filed in 2001.

More than 16,000 plaintiffs are claiming 80 million euros ($87 million) in compensation for a drop in the share price of the former state monopoly after they bought stock in a third tranche of shares to be offered in 2000.

The lead plaintiff in the case - Germany's closest thing to a class action in which one person is used as an example for all the others - has meanwhile died, but this does not affect the lawsuit.

About 70 percent of the 200 million shares on offer at 66.50 euros apiece in 2000 were bought by retail investors, who considered it a safe and stable investment. The public share sale, which began in 1996, was Germany's largest IPO to date.

Only eight months later, Deutsche Telekom announced a write-down on the valuation of its real estate portfolio, sparking a slide in the shares, which now trade at around 13 euros.

Germany's supreme court ruled almost two years ago that Deutsche Telekom failed to adequately inform potential investors buying shares in its public share offer at the height of the tech market bubble in 2000.

The supreme court referred the case back to the regional court in Frankfurt, which will now have to establish whether Deutsche Telekom will have to pay damages and if so how much.

(Reporting by Peter Maushagen; writing by Harro ten Wolde; editing by Jason Neely)