Mormons- a question about writing missionaries letters?

Can you just write any random missionary a letter? Just for a little service activity? I'm trying to become stronger in the gospel as I just got baptized a couple weeks ago (even though I've known the church my whole life) and I think it could be beneficial to share my conversion story with a missionary to encourage him/her to reach out to those "unlikey" people like I was at the time... I think missionaries are so incredible and I'd love to show my support to even one! So would it be weird if I just randomly picked one from the Dear Elder website? Haha I so don't know the protocol for this kinda thing..thanks in advance!:)