If I never signed a contract with an employer can he sue if I started my own company that indirectly competes with his?

Based on the information provided, it does not appear that your former employer may sue you successfully for starting your own company as long as you are not using trade secrets of the former employer or engaged in other conduct that violates some duty you may owe to the former employer. Of course, your former employer may sue you--it is simply a question of whether you will prevail. And without knowing all of the facts, it is not possible to definitively answer your question. 

Anyone can sue, but, assuming that you were just an employee and never an owner of your former employer, did not use your former employer's resources to start your competing company, have no valid agreement not to compete, and are not using trade secrets belonging to your former employer in your new business,  you have every right to compete using lawful means.