Just about everyone's had a time when they joined a roleplay only to have the rest of the players in it play on like they weren't even there. Yes, it's happened to me, too.
There will ALWAYS be situations where it happens. But there are ways to lower this risk!
1. Remember that it isn't about your character, but about the group.
A common mistake people make when joining an existing thread is expecting the group to drop everything they're doing to focus all their interest on the new character, sometimes when the new player has their character do little or nothing to warrant attention. This is one of the top reasons players wind up "ignored." Remember--their attention is already focused on something else when you step in. You'll have much better success if your character steps in expressing an interest in THEM and the existing situation. Pay attention to the story. Make sure your character can easily interact--even if they're shy, you can make a show of them fidgeting and stammering, right? If the other characters are talking about going hunting, have yours ask to join, or offer to lead or help the hunt. If a character is hurt, have yours try and help. If your character has no mate, and there's a possible crush there, that's another option--even if it doesn't wind up with a mate, it gets you into the action. {And if you want a mate more quickly, see #4.

} People like it when others give them attention, so make sure you do this when you join someone else's thread.
2. Join multiple threads! The more you join the more likely one is to stick. Be careful not to join too many or you won't be able to devote any meaningful time to any of them, though. A good amount when you are searching around is 5 or 6 active threads. Avoid threads that are too fast-moving and have many people in them {more than 4 or 5 people posting daily, generally} as you're less likely to be noticed when the action is fast-moving than if it is slower. The ideal number of people in a single thread to be posting in it daily is from 2 to 4 or 5. More than that, and things get chaotic!

Look around for threads that are asking for players to jump in to play a certain part, like a newborn kit, or empty Clan position. Ask if the spot is still open. That gives you a much easier in on the action and makes another member very grateful =)
3. Join chats! Also feel free to start your own. They can be found
here and
here.
Join a few of the smaller ones labelled open. Start your own as well, of course.
Why chats, when you're here to roleplay? Well, the chats are how you can meet other roleplayers and find buddies who'd like to partner or group up for a story. Just
don't go into someone ele's thread asking them to join your clan or roleplay--it comes off as spammy and annoying.
4. Try the
find-a-mate board, either general or advanced, depending on your preferences. Finding someone new to take up a relationship roleplay with one of your characters can form a solid foundation. If the mate roleplay leads to kits, you can offer two or three of them up for adoption by other players in the adoption board. You now have a family roleplay, with players in a ready-made plot.
Or so we hope. Which brings me to....
5. Keep an interesting plot or plot elements going. Make your characters want something badly. Give them issues. People are much more likely to remain interested in roleplays with DRAMA in them! Happy perfect characters get boring quickly. Fortunately the roleplay world is unlimited in options. When one conflict ends, make sure another starts. Injuries, jealousy, revenge, illness, kidnappings, the list goes on for plot devices!
6. Don't get frustrated if your first attempts flop! Keep bumping your threads if they leave the front page, if one chat fizzles try another. {We're not running out.} If you've been struggling with this for weeks, you can even ask for help in the help den. I sure wouldn't want anyone to feel left out of the fun.