How to place words horizontally vertically and diagonally in a Word Search game?

I have an 11 x 11 matrix in which I want to place 8 random words of any length (0-11). Words should be placed:

• horizontally in both directions

• vertically in both directions

• diagonally in all four possible directions

Words can cross over each other if they have one common character.

Words are to be picked from database on run time therefore there is not enough prior knowledge of what and how long the words would be. I have been busting my head for a few days now but still not able to complete the algorithm. Any assistance in this regard would be appreciated. Please mention if there is any free API on Unity Asset Store that can help me in this.

Thanks.