Whatever you do, do it WELL.
For my first sex scene in my comic I chickened out and legit did a one-panel sex scene. I still laugh about it. It probably did more harm than good. I later realised I had shorted not only the characters, but the readers, who had grown to care for these characters. I went back and edited the scene with another page ^^;
Now.
If it's a scene with characters well-known and loved by your fans, don't short them. If you've been building up these characters and their relationship, and If it's important to show it, you should be true to the characters and the story. It can be incredibly difficult to draw if you are not used to it, but it's also a good challenge. I recently did another, and a much more important one than the one-paneler, and it took a looooot of drafting. I had a friend look it over first, too, which I often don't do. Maybe do that? As for what to draw, focus on things like hand-holding, touching, kissing. Insinuate action but you don't have to show it. Fade in and/or out of the scene to make it seem as though there is more (but we are not going to see it).
And for the love of all that's good, keep goofy sound effects (like 'thrust') far away from your comic.
If it's a scene of characters we don't know well yet, or if it's their introduction scene.... Honestly, since I don't have emotional investment in their story or them as characters, less really IS more. I think I would be wondering why a creator chose to open up a scene or introduce two or more characters like this. Maybe if you want to establish they are sexual right off the bat or something. Keep it very short in that case.
You may turn away readers either way.
That can't be helped. As long as you've been writing well, your readers probably suspect it'll happen. People can generally tell what a comic or story is about upfront based on your story's tone, so as long as it's not a total surprise, it won't be jarring for readers.
It's strange we worry about this so much. I sure do. Yet people get kicked unconscious; shot with arrows; hell, there's a blood mage in my story. Yet heaven forbid the intimacy!