Thevis, who is based at the German Sports University in Cologne, told the Tackling Doping in Sport 2012 conference in London, presented by the worldsportslawreport, that the list of "80, 90, 100" new drugs similar to EPO was not exhaustive.
"They act like EPO but they are structurally different and that means the current EPO tests will not pick them up," he said.
"Fortunately we know about that problem and we have to develop new tests to help to find these drugs that, according to anecdotal evidence and rumours, are already used in elite sports although they are not officially launched yet.
"You cannot go to a pharmacy to buy these drugs. You might have (to have) good connections to get hold of those.
"It is quite difficult to develop tests when you don't have an idea what the molecule really looks like. If you don't know what the molecule looks like it's almost impossible to have a potential strategy."
EPO, which increases the number of red blood cells, has been used mostly by endurance athletes such as middle and long-distance runners and cyclists. A blood and urine doping test was introduced for the 2000 Sydney Olympics.
Anna Baoutina, a senior research scientist at the National Measurement Institute in Sydney, told the conference tests had been developed for detecting gene doping, defined by the World Anti-Doping Agency as the use of cells, genes or genetic elements to improve athletic performance.
"The major advantage of gene doping is that it's very difficult to detect compared to drug doping," she said. "The doping gene is very similar to the natural cells which are found in any body."
Baoutina said no test would be in place before this year's London Olympics.
"We are developing methods to fight it," she said. "But we have yet to see the implementation of these methods. WADA has to decide when these methods should be implemented."