Lille have prospered since Seydoux became their major shareholder in 2004, winning their first league title in more than 50 years in 2011 and moving to a new stadium in August.
However, the 65-year-old film producer, who owns a 54 per cent share, said in April he wanted to sell his stake within the next couple of years as he feared becoming a "silly old" president.
"I commissioned a firm last week to help me look for a partner or a buyer," Seydoux told daily L'Equipe on Friday.
"I always said I was looking for someone. It is the only solution to stay competitive and to make the club grow."
Lille have been one of the best French clubs for years but they still struggle in Europe, blaming financial gaps with the strongest European sides.
They are bottom in their Champions League group after four losses in four games, including a 6-1 rout at Bayern Munich on Wednesday.
Eighth-placed Lille host mid-table Stade Brest on Saturday, hoping to continue their Ligue 1 recovery after a dismal start.