I install SeaMonkey inside my /home directory (have always done it this way) and in order to launch it, I have to go into the file manager and migrate to the directory.
There are a couple ways to get a launcher going for you.
First of all since you installed Seamonkey to your /home directory you will have nothing in /usr/share/applications as suggested above.
I did a similar install and searched for the .desktop extension and did not find any.
So the best thing to probably do is make one.
Open the Adie editor in
enter the following as written except where all caps. There you will use your own username and the name of the file you have Seamonkey in.
Change the directory to Desktop
Click File --->Save As and save using the name "seamonkey.desktop