E.ON and RWE npower are looking for a new owner for Horizon Nuclear Power, the joint firm to develop Wylfa B.
Experts, politicians and community leaders say they are hopeful a new buyer can be found.
However, opponents to the Wylfa plans say alternatives to nuclear energy should now be found.
The German-owned companies blamed the global economic crisis, developments in the nuclear industry in Germany and what they called the "significant ongoing costs" of running the Horizon joint venture for the decision.
The Wales Green Party welcomed the decision, claiming it would help renewable industries.
Pippa Bartolotti, leader of the Wales Green Party said the costs of "unwanted nuclear sites were always going to be unsupportable".
"Germany and Japan know the price is too high for the environment. With new nuclear going way over budget and with no safe build in sight, we can at last reflect on the wisdom of using this type of energy.
"The intelligent way forward is to invest in renewables such as solar energy, tide energy and wind energy. Green energy will always provide us with more jobs, safer living and greater energy security."