Here are two animated GIFs which are free for you to use.
I made the Happy Birthday one last week, after I printed up a bunch of birthday cards ready for the year. Because each one came out slightly different, they make for an interesting animation when scanned and joined together. I can tell you in advance that this does not render very well in WhatsApp – I don’t really know why.
The I Love You one is from 2001, and it renders really nicely.
Use them for whatever you want. After all at some point it will be someone’s birthday, and everyone wants to know someone loves them, don’t they?